test(client): Agent Skills — the filesystem abuse matrix (5/5) by XieX · Pull Request #54 · launchdarkly/python-ai-sdk

XieX · 2026-08-25T20:17:40Z

PR 5 of 5 splitting draft #45 for review. Stacked on #53. This is the tip of the stack — its tree is #45's, plus the changes for review findings 1, 2 and 3 and the new safe_fs unit tests.

main ← #50 ← #51 ← #52 ← #53 ← split/skills-fs-hardening

Note

Aug 28: rebased in place for the stack-wide bytes pivot (Skill.content: bytes, frontmatter() deleted). Test helpers here construct Skill values from encoded bytes now; the defenses under test are unchanged. This branch also carries the rename-containment assertion fix cherry-picked across the rebase.

What's here

Tests only, no source. The adversary: every filesystem defense PRs 3 and 4 introduced now has a test that fails if the defense is removed.

Path traversal — a key that escapes the root, a key that is the manifest filename, an over-long key, and a key that resolves outside after realpath. Each refused before any filesystem call, and the containment check asserted on inode identity rather than on path strings.
Symlink attacks — a symlinked skill directory, a symlinked target file, and <root>/<key> swapped for a symlink at the exact instant of the rename and of the unlink. That last one is the narrowest possible version of the window descriptor pinning exists to close, fired from the interception point (os.replace / os.unlink) rather than from implementation internals.
The no-*at() shape — the path fallback Windows takes for every operation, exercised with the capability probe forced off, so the platform that cannot pin a descriptor is not the untested one. The TOCTOU tests skip off that same flag deliberately: a probe that wrongly reported "unsupported" must not also silently skip the tests that would have caught it.
Non-regular files and clobber protection — a fifo or a directory where SKILL.md belongs, and a file at a managed path with no matching manifest entry: reported and left alone, never overwritten and never removed.
Corrupt manifests — unreadable, unparseable, not an object, malformed entries, and a manifestVersion this release cannot read. No overwrites, no prunes, an error action naming the manifest, and the manifest itself left as it was found.
Atomicity — a crash injected between the write and the rename leaves neither a partial file nor a temp file, and the one recorded rename is proved to have moved SKILL.md within the target's own directory. Where the platform has renameat that is asserted by descriptor identity (src_dir_fd == dst_dir_fd, resolving to the skill directory's (st_dev, st_ino)), which is stronger than comparing path strings because it also rules out the descriptor having been redirected between the check and the rename.
Telemetry — the three signal names are asserted as an allowlist, not a floor: any other name reaching the emitter fails the test. The two deliberately excluded names are called out explicitly rather than left to the subset check. No signal carries a filesystem path or the skill body, an emitter that raises never fails the reconcile, and client.track() is never reached.

Notes for reviewers

Two cases are worth naming, because the obvious test does not reach the guard:

The unencodable-content cases pin contentHash to the sha256 of the bytes a non-strict encoder would have fabricated. An arbitrary wrong hash is rejected by the mismatch check first and never exercises the encoder guard at all, so a naive test here passes against an implementation that reaches for errors="surrogatepass".
The redaction cases smuggle the body through contentHash and through key. A sweep using a well-formed digest under a valid key reaches neither replacement branch.

The set of tests in test_skills_fs.py at this tip matches #45's modulo the bytes pivot (helpers build Skill.content as bytes; the deleted frontmatter() tests were removed in PR 1) — nothing else was dropped in the split. Two classes are reordered, which is why the file shows more diff churn than the content change warrants.

Testing

uv run pytest → 1280 passed. ruff check, ruff format --check, and mypy packages/*/src all clean.

🤖 Generated with Claude Code

Note

Overview
This PR expands Agent Skills from in-memory/test usage to production delivery and safer disk materialization, with matching public API and documentation.

Retrieval: Adds get_skill_result and frozen SkillOutcome / SkillOutcomeReason so callers can distinguish absent skills, wrong versions, store outages, and integrity failures (for fail-closed startup) while get_skill keeps returning None for all failures. Internal Resolution now carries an explicit reason mapped to those tokens.

Delivery: Introduces FDv2SkillStore (poll/stream against LaunchDarkly FDv2, wire-key key:version translation, payload commit semantics, diagnostics, server-side credential checks) and watch_skills / SkillWatcher to re-run write_skills on store listener events (debounced worker thread). InMemorySkillStore gains remove_listener for watcher cleanup.

Materialization / safe_fs: Rejects Windows reserved device names at write time on all platforms; adopts unmanaged files whose bytes already match resolved content (crash recovery); sweeps orphan temp files via shared is_temp_name / temp_name_prefix; bounds adoption reads to max_bytes + 1. Docs spell out POSIX descriptor pinning vs Windows TOCTOU and privilege-separated deployment.

Tests: Extensive TestGetSkillResult, listener removal, and export/immutability coverage in test_skills.py, plus large README/agents.md updates.

^{Reviewed by Cursor Bugbot for commit b62571e. Bugbot is set up for automated code reviews on this repo. Configure here.}

``test_key_at_the_data_model_bound_is_reported_not_raised`` read ``dst_dir_id`` directly, but that field is only populated when ``os.replace`` is called with ``dir_fd`` kwargs. On the path fallback (``SUPPORTS_DIR_FD`` false — the shape Windows takes) it stays ``None``, so the assertion failed even though the valid skill had been renamed correctly into its own directory. ``_assert_atomic_rename_of`` already branches on both call shapes and asserts the same containment property, plus the single-rename count the list comparison implied. Use it. Verified by forcing the probe off for a whole session: this was the only test in the module that broke under the no-``*at()`` shape, and the helper-based check passes under both. Reported by Cursor Bugbot on #54. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

cursor

Stale Bugbot comment from a previous run.

Fifth and last of five slices. The adversary. Every filesystem defense the previous two slices introduced now has a test that fails if the defense is removed, plus the materialization telemetry allowlist. - **Path traversal.** A key that escapes the root, a key that is the manifest filename, an over-long key, and a key that resolves outside after `realpath` — each refused before any filesystem call, and the resolved containment check asserted on inode identity rather than on path strings. - **Symlink attacks.** A symlinked skill directory, a symlinked target file, and the `<root>/<key>` directory swapped for a symlink at the exact instant of the rename and of the unlink — the narrowest version of the window the descriptor pinning exists to close, fired from the interception point rather than from implementation internals. - **The no-`*at()` shape.** The path fallback Windows takes for every operation, exercised with the capability probe forced off, so the platform that cannot pin a descriptor is not the untested one. The TOCTOU tests skip off that same flag deliberately: a probe that wrongly reported "unsupported" cannot also silently skip the tests that would have caught it. - **Non-regular files and clobber protection.** A fifo or a directory where `SKILL.md` belongs, and a file at a managed path with no matching manifest entry — reported and left alone, never overwritten and never removed. - **Corrupt manifests.** Unreadable, unparseable, not an object, malformed entries, and a `manifestVersion` this release cannot read: no overwrites, no prunes, an error action naming the manifest, and the manifest itself left as it was found. - **Atomicity.** A crash injected between the write and the rename leaves neither a partial file nor a temp file, and the one recorded rename is proved to have moved `SKILL.md` within the target's own directory — by descriptor identity where the platform has `renameat`, which also rules out the descriptor having been redirected between the check and the rename. - **Telemetry.** The three signal names are asserted as an allowlist rather than a floor: any other name reaching the emitter fails, the two deliberately excluded names are called out by name, no signal carries a filesystem path or the skill body, an emitter that raises never fails the reconcile, and `client.track()` is never reached. Two of these are worth naming, because the obvious test does not reach the guard. The unencodable-content cases pin `contentHash` to the sha256 of the bytes a non-strict encoder would have fabricated, since an arbitrary wrong hash is rejected by the mismatch check first and never exercises the encoder guard. The redaction cases smuggle the body through `contentHash` and through `key`, since a sweep using a well-formed digest under a valid key reaches neither replacement branch. Testing: `uv run pytest` → 1280 passed. `ruff check`, `ruff format --check`, and `mypy packages/*/src` all clean. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

``test_key_at_the_data_model_bound_is_reported_not_raised`` read ``dst_dir_id`` directly, but that field is only populated when ``os.replace`` is called with ``dir_fd`` kwargs. On the path fallback (``SUPPORTS_DIR_FD`` false — the shape Windows takes) it stays ``None``, so the assertion failed even though the valid skill had been renamed correctly into its own directory. ``_assert_atomic_rename_of`` already branches on both call shapes and asserts the same containment property, plus the single-rename count the list comparison implied. Use it. Verified by forcing the probe off for a whole session: this was the only test in the module that broke under the no-``*at()`` shape, and the helper-based check passes under both. Reported by Cursor Bugbot on #54. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

…esystem can hold Two gaps from the Agent Skills security design review, both in `skills_fs.py`: AV-3 (partial reconciles are unrecoverable) and DV-2 (the key grammar admits Windows device names). **AV-3 — adopt a file whose bytes already are the resolved content.** `_write_all` reconciles every skill and only then rewrites the manifest, once, last. A process killed in that window leaves a skill file at a managed path with no manifest entry — exactly the condition `_write_one` treats as an unmanaged-file collision, so the skill was wedged permanently: every later reconcile took the same refusal branch. Boot-time execution under a ten-second budget makes the crash window realistic. `_write_one` now reads and hashes first and decides from the bytes. Content byte-identical to what LaunchDarkly resolved is adopted — manifest entry recorded, reported `skipped_current` — and anything else falls through to the same refusal as before. This cannot weaken the clobber guarantee: differing unmanaged bytes are never overwritten, and the existing clobber tests pass unchanged. Three details carry the safety: - A read that fails is a refusal, never an overwrite, with a message distinguishable from the byte-mismatch refusal — it is the comparison that would otherwise authorize the write, and a file that could not be read has not been shown to be ours. - The read stays on `_read_regular_file`. Adoption widens it to genuinely foreign files, so its refusal of FIFOs and other non-regular files is now load-bearing rather than defensive. It gains a `max_bytes` bound of `len(content) + 1` — enough to prove inequality for anything longer, and what keeps a foreign file of arbitrary size out of memory. A bound of exactly `len(content)` would adopt every file that merely begins with the resolved content. - `skipped_current` is reused rather than adding an `adopted` action kind, so `ReconcileActionKind` — public, and owned by an approved PR — does not change. Its documented meaning already fits. Adoption also makes the file prunable later. That is correct rather than a weakening: only byte-identical LaunchDarkly content is ever adopted, so a later prune removes content LaunchDarkly delivered anyway — what would have happened had the crash not occurred. The review also floats a write-intent journal. Assessed as over-engineered; not built. **AV-3, secondary — sweep orphaned temp files.** `atomic_write` unlinks its temp file on any exception but not after a `SIGKILL`, and `_prune` walks manifest entries, which an orphan never has, so nothing would ever notice one. The second-order effect is worse than the disk: `_prune_one`'s `rmdir` only succeeds on an empty directory, so a single orphan pins a skill's directory forever. The sweep runs on both the write and the prune path, and is the one place this SDK removes a file the manifest does not list, so it is bounded on every axis: inside `<root>/<key>/` only, for a key that passes `_key_rejection_reason`; only names `safe_fs` itself recognizes, via a new `is_temp_name` beside the naming code rather than a copy of the format string that could drift from it; only regular files, with the type read off the descriptor; unlinked through the pinned descriptor. It never raises and never aborts a run. **DV-2 — reject the 22 Windows reserved device names.** `con`, `prn`, `aux`, `nul`, `com1`–`com9`, `lpt1`–`lpt9` are all valid skill keys and none can be a directory name on Windows. Rejected in `_key_rejection_reason`, which the write and prune paths already share, and *not* in the key grammar: `parse_ai_config` fails closed, so a grammar-level rejection would invalidate an entire AI Config for a Linux customer over a Windows-only constraint, and would silently shrink `skill_refs` — which is what authorizes a prune, turning "fails to write on Windows" into "gets deleted on Linux". The 255-byte component bound is in this layer for the same reason. Unconditional, not platform-gated: a root written from a Linux container is routinely read from a Windows host, and neither repository has a Windows CI runner, so a gated branch would be untestable — the condition that produced the gap. No suffix stripping and no case folding: the grammar admits no `.` and no `$`, so `con.txt` and `CONIN$` are unreachable, and keys are lowercase-only. `com0` and `lpt0` are not reserved and are not included. The trade is real and belongs in the release notes: a customer who legitimately names a skill `aux` now gets a reported `error` action on Linux where it previously worked. Neither gap emits the integrity-failure log record. A key rejection and a clobber refusal are `ReconcileAction` errors, not integrity failures. Tests cover crash-mid-reconcile recovery end to end (adopted, reported, recorded, and the next reconcile an ordinary no-op), byte-differing content still refused untouched, an unmanaged FIFO refused without hanging, a read failure refusing rather than overwriting, the `len + 1` off-by-one, the sweep and the `rmdir` it unblocks, lookalike temp names and a symlink wearing one left alone, all 22 reserved names through both destructive paths, and — the point of the layer choice — each reserved name still valid to `is_valid_skill_key`, `parse_ai_config`, and `skill_refs`. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

…failure ``get_skill`` returns ``None`` for four unrelated outcomes: no such skill, the store raised, the requested version is not the one held, and content that failed hash verification. A caller cannot fail closed on suspected tampering while tolerating a merely-absent skill, so no automated customer-side response is possible — finding LA-2 of the Agent Skills security design review. The information already existed internally, as prose in ``Resolution.error``. This gives it a token: ``Resolution`` grows a typed ``reason``, set explicitly at every construction site and declared without a default so a sixth outcome added later has to choose which public token it maps to. ``get_skill_result`` maps that straight through to a frozen ``SkillOutcome`` (``skill``, ``reason``, ``detail``). Deriving the public reason by matching the error string is the fragility LA-2 is about, so the mapping is readable in one table. ``get_skill`` is untouched — its ``None``-for-every-failure contract is documented in its docstring and in the README, and a test now pins that all four failures still collapse to ``None`` and still never raise. Nothing new is emitted: Gap 1's integrity record already fired inside verification before ``resolve_from_store`` returned, and a test asserts one failed retrieval still produces exactly one record and one signal. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

… remainder The four items left open in the response to the Agent Skills security design review. Three are documentation, one is tests; no behavior changes, and the code halves of rows 9 and 2 are deliberately untouched. **Privilege separation** (row 9 docs half, and the agreed counter-proposal for row 26). The recommended deployment runs the reconcile as a different identity than the agent, which is the whole reason the ``0644``/``0755`` modes deny anything: the agent reads its instructions and cannot rewrite them, or the manifest. That is the mitigation for AZ-1, a prompt-injected agent editing its own skills. Write access to the manifest is the worse half — it is what tells the *next* reconcile which paths the SDK may delete — which is why ``_prune`` re-validates every entry from scratch rather than trusting it. The README documents the pattern and hands the operator the check to run, because the SDK cannot run it: it knows only its own identity, which trivially has write access, having just written there. So ``ReconcileReport`` grows no writability field — the review asked for one and we declined, since any check the SDK could make would answer a different question than the one asked and manufacture false confidence exactly where caution is wanted. ``agents.md`` records that reasoning so the field is not added later by someone reading its absence as an oversight. **Three hostile-manifest prune tests** (row 12 remainder): a well-formed manifest listing ``/etc/passwd``, ``../../../etc/passwd``, and a path under a parent that has since become a symlink. ``_prune`` already refuses all three, so these turn asserted into verified. Two things make them worth more than their line count. They are deliberately *well-formed* — the corrupt-manifest suite above them proves nothing here, because a corrupt manifest suppresses every destructive action wholesale, whereas these manifests give the implementation everything it needs to prune. And "deleted nothing" is asserted through an unlink spy rather than by checking that ``/etc/passwd`` still exists: the test process cannot delete that file anyway, so the obvious assertion would pass against an implementation with no path check at all. **One sentence on** ``"*"`` (row 16 remainder). It materializes the whole project library, so every skill's ``description`` enters the agent's context — including skills no AI Config references and skills belonging to other teams. **The Windows platform bound is now explicit** (row 2 residual), in ``safe_fs.py``, ``agents.md`` and the README. Reparse-point checks (``GetFileAttributesW`` / ``FILE_FLAG_OPEN_REPARSE_POINT``) are not implemented, by decision: Windows is not a supported or tested platform for this release, neither repository has a Windows CI runner so the checks would ship unverified, and the TypeScript SDK could not match them in any case because Node exposes no ``*at()`` family on *any* platform. Implementing them in Python alone would break cross-language parity and trade a documented bound for an unverified one. Two consequences are recorded rather than left to be rediscovered: on Windows, write permission on the managed root is the only boundary, which is what makes privilege separation the mitigation and not merely advice; and this retroactively lowers the priority of the row 25 reserved-device-name work, noted where that code lives. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

write_skills is a one-shot reconcile, so a revocation takes effect at the next process restart. watch_skills runs that reconcile now and again whenever the configured store reports a change, so a revoked skill's files leave the disk within a debounce interval of the store learning about it. It is wired to the SkillStore interface, not to any one transport: it needs a store that implements add_listener and nothing more, and refuses loudly when the store does not, since a watcher that silently never fires looks exactly like one whose skills never changed. Above the interface, remove_listener joins add_listener as the optional second half of change notification, on the SkillStore contract and on InMemorySkillStore. SkillWatcher.close needs it to detach; without it a store held every watcher ever created for the rest of its life. The watcher probes for it, so a store without it keeps working. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

…network The half of the delivery transport that has no I/O: identifying a skill object on the wire by kind inline-resource plus category skill, translating it into the raw object shape the SkillStore interface defines, holding it by (key, objectVersion), and applying a payload's events as one commit at payload-transferred. The store that puts a connection underneath this follows separately, so the three decisions that matter most can be reviewed on their own: - objectVersion is the skill's version; version is the payload's. The translation happens in one place and TestVersionTranslation asserts it in both directions, because confusing them fails silently. - Changes commit at payload-transferred, not per object. A half-applied full transfer would briefly empty the store, which with pruning on is the difference between a reconcile and deleting a customer's files. - A hashless object is held, not dropped, so verification withholds it with a reason code rather than the transport reporting it absent. Flag and segment objects share the connection and are skipped and counted, not rejected. Nothing here is exported yet; the store exports it. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

…oncile watch_skills awaited write_skills and only then constructed SkillWatcher, which is where the store listener attaches. The reconcile snapshots the store as its first step and then spends the rest of its time on the filesystem, so every write, fsync, prune and manifest rewrite in that first pass ran with nothing listening. A change delivered in that window was never seen, and since nothing re-reconciles on a timer, a revocation that landed there waited for the next unrelated change — on a quiet root, the next restart. Exactly the gap watch_skills exists to close. The watcher now attaches its listener before the initial reconcile and starts its worker after. notify only sets an event, so a change arriving mid-reconcile is recorded and picked up by the worker's first pass, while holding the thread back keeps write_skills's one-root-one-reconcile contract: the worker cannot race the caller's own reconcile over the same manifest. A reconcile that raises detaches the listener on the way out, since the caller is handed an exception rather than a watcher to close. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The protocol reader took payloads[0]'s intentCode and applied it to the skill object set, which is what the delivery protocol requires — one payload per credential, read the first intent, tolerate the rest — but it left the assumption behind that rule undocumented and unguarded. If the one-payload guarantee ever widens, an xfer-full for another payload would start an empty pending set and the next payload-transferred would publish it: every skill reported revoked, and with pruning on, a customer's files deleted. The first payload is still the payload that is read. What is new is that the reader now knows which payload skills actually arrive on — learnt from the intent's id, or from the (p:<id>:<version>) selector, since no object or transfer event carries a payload id of its own — and declines to apply a transfer of any other, holding last known good, warning once, and counting it in diagnostics.payloads_ignored. An intent describing more than one payload warns once on its own, because that is the one case the comparison cannot catch: another payload's transfer arriving before any skill has been seen has nothing to be compared against. Behaviour under one-payload delivery is unchanged, and a full transfer of the skill payload still empties it — every skill deleted is a real state the guard must not mask. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

The SDK-facing FDv2 channel now delivers skills the way streamer #4681 and gonfalon #70638 spell them: object kinds are open strings, the agent-skill payload is classified `generic`, and every generic object carries only `key`, `kind`, `version` and `object`, exactly like a flag. A skill arrives under kind `skill` with its own version folded into the key as `<key>:<version>`. There is no `category` field and no `objectVersion` field; both came from an earlier streamer draft that never shipped. Identification is now the kind alone. The wire key is split in one place, `_split_wire_key`, and both the put and the delete translation go through it. A key that will not split cleanly is held rather than dropped — version-less, or with the offending text as its version — so verification withholds it with `invalid_version` under a key the caller recognises; only a key with nothing before the delimiter is dropped, since there is no identity to hold it under. `SDK_DATA_MODEL_VERSION` goes with it: the connection's `mv` parameter only accepts flag model versions, and generic payloads ignore it. The transport stops sending it in the following change. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

FDv2SkillStore puts LaunchDarkly's SDK-facing FDv2 channel underneath the protocol layer: GET /sdk/poll and GET /sdk/stream, authenticated with the environment's server-side SDK key, streaming by default. It carries basis across requests, sends If-None-Match and treats 304 as a current answer, retries with capped jittered backoff, honours Retry-After only up to max_backoff, gives up after a bounded run of consecutive failures where a committed payload resets the count, and keeps serving last known good through every failure. A mobile key or client-side environment ID is refused in the constructor. Standard library only. close interrupts the socket rather than only setting a flag, because the delivery thread lives in a read no flag can reach; without that every shutdown of a healthy stream waited out the full join timeout. The no-store message now names FDv2SkillStore first, and watch_skills points at it as the store with a delivery transport. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

_Requester.stream wrapped only the connect as recoverable, so a read timeout, reset or truncated chunk in the body reached the delivery loop as whatever the socket raised. The loop read that as a bug and gave up: delivery stopped for the process lifetime, taking updates and revocations with it, the first time a socket died. read_timeout exists to bound a stream that has gone quiet so the loop can reconnect, and tripping it did the opposite. The body now carries the same promise the connect already did. Wrapping the line source rather than the whole read keeps protocol reader errors out of it: those are raised from the consumer's loop body, where they still surface as the bugs they are. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

…n promptly Three faults in the delivery loop, all of which left the store reporting itself healthy while doing less than it claimed. **An up-to-date stream tripped the failure cap.** The consecutive-failure count reset only at a commit, and an environment whose skills are not changing answers every reconnect with `intentCode: "none"` and transfers nothing. A stream only ever ends by being dropped, so each recycle of a perfectly healthy idle connection counted as a failure — announced with a `goodbye` or not — and `max_consecutive_failures + 1` of them stopped delivery for the process lifetime, revocations included. The reset on commit covered only the case where content had changed, which is the case that was easy to test and not the case that runs in production. `_TransferOutcome` now reports `up_to_date`, and a complete answer that transfers nothing breaks the row of failures exactly as a commit does. An intent this module does not recognise is still not an answer. **`close` could not interrupt a poll.** The interrupt reached the streaming connection only, so polling parked in its request with nothing to reach and `close` returned when its join timed out — on a 300s-class request, long after the process meant to exit. `_Requester` now tracks the response of a poll in flight and offers `interrupt`, which `close` calls alongside the stream's own. A request still inside its connect has no response to reach; that one is bounded by `read_timeout`, and `start` no longer leaves the store inert when a join times out around it. An interrupt we asked for is no longer recorded as a delivery failure. **`close` left a waiter parked.** `wait_for_skills` waited on the first payload alone, so a shutdown racing a waiter added the waiter's whole timeout to it. Delivery ending is now its own event: a waiter is released by a payload, a give-up or a close, and reports whether a payload actually arrived rather than merely that it was let go. That also settles what `_give_up` had been quietly asserting — it set the first-payload flag to unblock waiters, which made `wait_for_skills` answer `True` for a store holding nothing. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

A stream only ever ends by being dropped, and LaunchDarkly — and any proxy in between — recycles a long-lived one. Every reconnect therefore logged "Skill delivery failed" at WARNING, for as long as the process ran. Until the previous commit that noise was bounded, because an idle stream gave up after eleven recycles and went quiet; now that delivery correctly survives them, it would run forever and describe a healthy store as failing. A connection that got a complete answer before it ended — a committed payload, or an up-to-date intent — delivered everything it was asked for, so its reconnect is now DEBUG and says so. A connection that ended without answering is the case the warning exists for and still gets it: a connect that never landed, or a transfer that died part-way through. Filling a customer's logs with a fault they do not have is not merely untidy; it teaches them that the level which means something can be ignored. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Stacked on the protocol-layer PR (`xie/skills-fdv2-protocol`). Third of three PRs split out of #69, and the one that makes the feature real: the network underneath the protocol reader, exported as `FDv2SkillStore`. ## Why this shape Skill content arrives over `GET /sdk/poll` and `GET /sdk/stream`, authenticated with the environment's server-side SDK key. These are the SDK-facing endpoints the base SDK's FDv2 data source uses, and the channel that payload signing will eventually cover. No private route is involved, and no credential other than the environment's own SDK key ships to a customer host. Standard library only, so the content path adds no dependency to a package whose sole runtime dependency is `opentelemetry-api`. ## What's here **`FDv2SkillStore`.** Authenticates, streams (default) or polls, carries `basis` across requests, sends `If-None-Match` and treats 304 as a first-class current answer, and serves `get_object` / `all_objects` / `add_listener` / `remove_listener` from what the protocol reader has committed. Capped jittered backoff; `Retry-After` honoured but clamped to `max_backoff` and rejected when non-finite; bounded consecutive-failure retries, where a committed payload resets the count. One network timeout, `read_timeout`, whose default follows the mode: 10s for a whole poll, 300s between reads on a stream. A mobile key or client-side environment ID raises from the constructor. Last known good survives every failure; `diagnostics` and `failed` report the degradation. **`close` interrupts the socket.** The delivery thread parks in a read no flag can reach, and closing a urllib response from another thread does not unblock CPython's buffered reader, so `_interrupt_read` shuts the socket down underneath it. Without that every shutdown of a *healthy* stream blocked for the full join timeout. **Above the interface**, two strings: `NO_STORE_MESSAGE` now names `FDv2SkillStore` first, since it is the first thing a user sees on a missing store and offering only the development store was wrong once a production transport existed; and `watch_skills`' refusal message names it as the store with a delivery transport. ## Bugs found and fixed while testing the loop Five, all sharing one shape: the store stopped delivering while continuing to report itself healthy. - **The consecutive-failure counter never reset in stream mode.** `_stream_once` always ends by raising, so a reset on return was unreachable and `failures` grew for the whole process lifetime. Eleven *fully successful* payload transfers were enough to trip `max_consecutive_failures` and stop delivery for good, revocations included. A commit now resets the count, in `_apply`. - **A non-finite `Retry-After` killed the delivery thread.** `float("inf")` parses, and `Event.wait(inf)` raises `OverflowError` from inside the recoverable-error handler. Non-finite values are rejected and every honoured delay is clamped to `max_backoff`. - **`close()` during the initial connect waited out its full join timeout.** `self._connection` was assigned after the connect returned, so a `close()` in that window found nothing to interrupt. The stop flag is re-checked immediately after the assignment. - **`close()` blocked for the full join timeout on every healthy stream.** See `_interrupt_read` above. - **A stream interrupted by our own `close` was reported as a delivery failure.** Also: `connect_timeout` was accepted and never used, so a poll against a black-holed host hung for 300s rather than 10. It is gone, with the request timeout now chosen by mode, and `TestTimeouts` measures the bound against a socket that accepts and never answers. ## Tests > **Rebase note.** The previous push of this branch had silently reverted the protocol PR's last commit (payload identity: `payloads_ignored`, `_is_foreign_payload`, `TestPayloadIdentity`). Rebasing onto the updated protocol branch restored it; the full suite passes with it present. `_FakeFDv2Endpoint` is an in-process `ThreadingHTTPServer` implementing the wire contract, so request construction and header handling are exercised over real sockets rather than mocked. Covers skill put/delete over the wire, mixed payloads, 304, `basis` round-tripping, reconnect/backoff in both modes, `Retry-After` including non-finite and oversized values, bounded retries and the reset on commit, prompt shutdown during connect and during a healthy stream, hashless envelopes end to end through the accessors, server-side-only credentials, timeouts, and `watch_skills` over the transport: a wire-level revocation pruning a file without a restart. Full suite 1629 passing, 11 skipped; `ruff`, `ruff format`, and `mypy` clean. ## Open items, none in this PR's scope - 🔴 **`contentHash` is not on the wire yet.** Against a real environment today every skill resolves to nothing. This PR makes that loud (an error per hashless object, a summary per wholly-hashless payload, `diagnostics.hashless_objects`) rather than surviving it. - 🔴 **Server-side skill delivery is not deployed.** The wire shape this store reads — kind `skill`, key `<key>:<version>`, generic payload — is what [streamer #4681](launchdarkly/streamer#4681) and [gonfalon #70638](launchdarkly/gonfalon#70638) emit; both are still open. No account can receive skill objects until they ship and the producer is enabled. - 🟡 **FDv2 is opt-in per account.** A real environment returns 403 today; the store reports it as fatal and explains what to do. - ~~🟡 **`mv` is a guess.**~~ Resolved: the request sends no `mv`. That parameter selects the *flag* data model and the connection rejects any value but the flag default, while the generic agent-skill payload is served regardless of it. The `data_model_version` constructor argument is gone with it. - 🟡 **No payload signing** on this channel yet, so Beta is TLS-only. - 🟡 **The connection also carries the environment's flags.** Skipped and counted; a transport property, not fixable here. - 🟡 **`ld-relay` does not speak the FDv2 endpoints**, so relay-only deployments cannot receive skills in Beta. **Nothing here has touched a real LaunchDarkly environment**, because it cannot yet. 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Overview** > Adds **`FDv2SkillStore`**, a production `SkillStore` that pulls agent skills over LaunchDarkly’s SDK FDv2 **`/sdk/poll`** and **`/sdk/stream`** endpoints (stdlib HTTP, background delivery thread, stream-by-default). It implements **`SkillStore`** (`get_object`, listeners, etc.) on top of the existing protocol reader, plus **`StoreDiagnostics`**, **`wait_for_skills`**, capped backoff with **`Retry-After`**, and **`close`** that interrupts blocked socket reads so shutdown is prompt. > > **Public surface:** `FDv2SkillStore` and `StoreDiagnostics` are exported from the package; README documents production setup with `init_client` and `watch_skills`. Server-side SDK keys only; mobile/client credentials are rejected. Outages keep last-known-good content; accessors above the store are unchanged. > > **Delivery-loop fixes** bundled here: reset consecutive-failure counts on successful commits / up-to-date answers (so healthy stream recycling does not stop delivery), safe handling of non-finite **`Retry-After`**, and not treating intentional **`close`** interrupts as transport failures. Removed unused **`connect_timeout`**; **`read_timeout`** is the single knob with mode-specific defaults. > > **Tests:** in-process fake FDv2 server exercises poll/stream, basis/ETag/304, revocations, retries, timeouts, hashless payloads, and **`watch_skills`** over the transport. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit 88c225e. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).

…network (#82) Stacked on the `watch_skills` PR (`xie/skills-watch`). Second of three PRs split out of #69; the transport that puts a connection underneath this follows. The half of the delivery transport that has no I/O: identifying a skill object on the wire, translating it into the raw object shape the `SkillStore` interface defines, holding it by `(key, objectVersion)`, and applying a payload's events as one consistent commit. Splitting it out lets the three decisions that matter most be reviewed without a socket in the way. ## Three things worth reviewing closely **1. The skill's version is in the object's `key`; `version` is the payload's.** Each version of a skill is its own object on the wire, identified as `<key>:<version>` (`pdf-extraction:3`), and that is the only place the skill's version appears. The event's `version` is the payload's, and confusing the two fails *silently*: the object verifies, the hash matches, and the caller gets content under a version number that means nothing. The wire key is split in exactly one place (`_split_wire_key`), both the put and the delete translation go through it, and `TestVersionTranslation` asserts it in both directions. A key that will not split cleanly is *held* rather than dropped — version-less, or with the offending text as its version — so verification withholds it with `invalid_version` under a key the caller recognises; only a key with nothing before the delimiter is dropped. **2. Changes commit at `payload-transferred`, not per object.** A payload version is the unit of consistency. A half-applied full transfer would publish a state the server never described and would briefly empty the store, which, with pruning on, is the difference between a reconcile and deleting a customer's skill files. An interrupted transfer leaves last known good intact, and listeners fire once per commit. **3. A hashless object is held, not dropped.** Dropping it at the transport would report `absent`, indistinguishable from "no such skill", and would let a prune delete the last known-good copy on disk. Holding it means verification withholds it with `missing_content_hash`, which is diagnosable: an ERROR per `(key, version)`, deduped per reader rather than per process so two stores never quieten each other, a summary per wholly-hashless payload, and a `StoreDiagnostics.hashless_objects` counter. There is deliberately no fallback that synthesises a hash from the delivered content. ## Also here - **Skills are `kind == "skill"`; everything else is ignored, not rejected.** Object kinds on the SDK-facing channel are open strings and the agent-skill payload is classified `generic`, so a skill arrives under the kind its producer registered — the bare category name — with no `category` or `objectVersion` field ([streamer #4681](launchdarkly/streamer#4681), [gonfalon #70638](launchdarkly/gonfalon#70638)). An environment's assignment carries its flag payload alongside its agent-skill payload, so flag and segment objects arrive as a matter of course. Erroring on them would turn a normal payload into a permanent reconnect loop. - **`_SkillObjectSet`** holds several versions of one key, with lookup semantics identical to `InMemorySkillStore` down to the fall-through to a version-less entry. Its opaque snapshot keys are spelt `<key>:<version>`, the same as the wire, and a test pins that round trip. `TestInterfaceParity` asserts the two resolve identically. - **`_require_server_side_credential`** refuses a mobile key or client-side environment ID. Its tests arrive with the store constructor that calls it. Nothing here is exported yet; the store exports it. The module imports nothing from the feature but the version validator. ## Tests `test_skills_fdv2.py` drives `_ProtocolReader` directly: identification, version translation, full and change transfers, interruption, revocation, tombstones, mixed payloads, unknown kinds and events, error and goodbye, and the hashless dedupe across readers. The wire builders it introduces are shared with the transport PR's fake endpoint. 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Overview** > Adds **`skills_fdv2.py`**, a stdlib-only layer below `SkillStore` that parses LaunchDarkly FDv2 events without sockets. It maps wire `put-object`/`delete-object` into the raw store shape, keeps skills in **`_SkillObjectSet`**, and applies updates atomically in **`_ProtocolReader`** at **`payload-transferred`** (not per object). > > The critical wire rule is **`key` = `skillKey:objectVersion`** while the event’s **`version` is the payload revision** and is dropped—confusing them would silently serve the wrong pinned version. Non-`kind == "skill"` objects (flags, segments) are **ignored**, not errors. **Foreign payload** full transfers are declined once skills’ payload id is known, so a flag `xfer-full` cannot wipe held skills (and trigger prune). **Hashless** skills are retained for verification to withhold with `missing_content_hash`, with **`StoreDiagnostics`** and loud logging. **`_require_server_side_credential`** rejects mobile/client credentials (for the upcoming networked store). > > **`agents.md`** documents the transport contract; **`skills_core`** clarifies `SKILL_OBJECT_KIND` vs wire kind. **`test_skills_fdv2.py`** (~900 lines) exercises the reader, version translation, payload identity, and parity with `InMemorySkillStore`. Nothing is exported or wired from accessors yet—that’s the follow-on transport PR. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit efc4ca7. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).

…ls (#81) Stacked on #66 (`split/skills-review-closeout`). First of three PRs split out of #69; the FDv2 protocol layer and the transport follow on top of this one. `write_skills` is a one-shot reconcile, so a revocation takes effect at the next process restart. `watch_skills` runs that reconcile now and again whenever the configured store reports a change, so a revoked skill's `SKILL.md` leaves the disk within a debounce interval of the store learning about it, rather than at the next restart. ## What's here **`skills_watch.py`** — `watch_skills` / `SkillWatcher`. Wired to the `SkillStore` interface, not to any one transport: it needs a store that implements `add_listener` and nothing more. It refuses loudly when the store does not, because a watcher that silently never fires looks exactly like one whose skills never changed. The listener itself only sets an event; the reconcile runs on a single worker thread, debounced, so a burst of changes coalesces into one pass and a slow disk never stalls the store's delivery thread. A reconcile that raises is logged and the watcher continues. `on_unavailable="keep"` stays the default: an outage must not read as "everything was revoked". **`remove_listener(kind, fn)`** joins `add_listener` as the optional second half of change notification, on the `SkillStore` contract and on `InMemorySkillStore`. `SkillWatcher.close()` needs it to detach; without it a store held every watcher ever created for the rest of its life. The watcher probes for it and skips detaching when a store does not implement it, so a customer's own store keeps working. ## Tests `test_skills_watch.py` drives the watcher through `InMemorySkillStore`, whose `put` notifies synchronously, and through small store doubles: initial reconcile, coalescing, refusal of a store without `add_listener`, detaching on close, and a store without `remove_listener`. Three tests on `InMemorySkillStore.remove_listener` join `test_skills.py`. The end-to-end case, a `delete-object` arriving over a live connection and pruning a file, lands with the transport PR where the fake endpoint lives. 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Overview** > Adds **`watch_skills`** and **`SkillWatcher`** so agent skill files stay in sync with the configured skill store without waiting for a process restart. The API runs an initial `write_skills` reconcile, then listens for store delivery changes and re-reconciles on a **debounced background thread** (listener only wakes the worker; disk I/O never blocks the delivery thread). Revocations can prune `SKILL.md` within the debounce window. **`on_unavailable="keep"`** remains the default so transport outages are not treated as mass revocations. > > Extends the optional **`SkillStore`** change-notification contract with **`remove_listener(kind, fn)`**, implemented on **`InMemorySkillStore`**, so **`SkillWatcher.close()`** can detach; stores without it still work but keep listeners registered. **`watch_skills`** raises if no store is configured or the store lacks **`add_listener`**, and cleans up the listener if the initial reconcile fails. > > Public exports and README/agents docs are updated; new tests cover watcher behavior (coalescing, mid-startup revocations, close/detach) and **`remove_listener`** semantics. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit 29ad3fe. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).

… remainder (#66) Stacked on #58. Closes the four items left open in [our response](https://launchdarkly.atlassian.net/wiki/spaces/PD/pages/5293965360) to the [Agent Skills security design review](https://launchdarkly.atlassian.net/wiki/spaces/PD/pages/5264506969). Three documentation items and one test item. **No behavior changes** — the code halves of rows 9 and 2 were already done and are deliberately untouched; the only change to `safe_fs.py` is its module docstring. ## 1. Privilege separation (row 9 docs half + counter-proposal for row 26) The proposed mitigation for **AZ-1**, the review's most serious finding. The README now documents reconcile-identity ≠ agent-identity as the recommended deployment, which is the whole reason the `0644`/`0755` modes deny anything: the agent reads its instructions and cannot rewrite them, or the manifest. Write access to the manifest is the worse half — it is what tells the *next* reconcile which paths the SDK may delete — which is why `_prune` re-validates every entry from scratch rather than trusting it. The operator gets an explicit check to run, because the SDK cannot run it. **`ReconcileReport` deliberately grows no writability field.** Row 26 asked for one; we declined. The SDK knows only its own identity, which trivially has write access, having just written there. Any check it could make would answer a different question than the one asked and manufacture false confidence exactly where the review wants caution. `agents.md` records that reasoning so the field is not added later by someone reading its absence as an oversight. ## 2. Three hostile-manifest prune tests (row 12 remainder) A well-formed manifest listing `/etc/passwd`, `../../../etc/passwd`, and a path under a parent that has since become a symlink. `_prune` already refuses all three; these turn asserted into verified. Two things make them worth more than their line count: - They are deliberately **well-formed**. The corrupt-manifest suite above them proves nothing here — a corrupt manifest suppresses every destructive action wholesale, whereas these manifests give the implementation everything it needs to prune, and it must refuse anyway because the recorded *path* is not one this SDK could own. - **"Deleted nothing" runs through an unlink spy**, not through checking that `/etc/passwd` still exists. The test process cannot delete that file anyway, so the obvious assertion would pass against an implementation with no path check at all — permissions would be doing the work. The spy proves the removal is never *attempted*. ## 3. One sentence on `"*"` (row 16 remainder) It materializes the whole project library, so every skill's `description` enters the agent's context — including skills no AI Config references and skills belonging to other teams. ## 4. Windows platform bound (row 2 residual) — deferred, explicitly **Decision: defer, with the bound written down.** Reparse-point checks (`GetFileAttributesW` / `FILE_FLAG_OPEN_REPARSE_POINT`) are not implemented, and that is now recorded in `safe_fs.py`, `agents.md` and the README rather than left implied. Rationale: - Windows is not a supported or tested platform for this release, and **neither repository has a Windows CI runner** — every matrix job is `ubuntu-latest` — so the checks would ship unverified. Both codebases already cite that absence as a reason not to add `os.name`/`process.platform` branches. - **The TypeScript SDK could not match them in any case.** Node exposes no `*at()` family on *any* platform, so its racy `lstat` floor is universal rather than Windows-only. Hardening Python alone would break the cross-language parity the two SDKs are held to. Two consequences are recorded rather than left to be rediscovered: on Windows write permission on the managed root is the *only* boundary, which is what makes privilege separation the mitigation and not merely advice; and this **retroactively lowers the priority of the row 25** reserved-device-name work, noted where that code lives. That code stays — it keeps a root written on Linux usable when read from Windows — but it is not evidence that Windows is hardened. ## Parity The Node half is launchdarkly/js-ai-sdk#48, case for case. No customer-visible surface moved: the `ld.skills.integrity_failure` event name, the eight `reason_code` tokens, the five `SkillOutcomeReason` tokens, and the log-record serialization are untouched. ## Verification - `uv run pytest` — 1484 passed, 11 skipped - `uv run ruff check .` / `ruff format --check .` — clean - `uv run mypy packages/*/src` (the CI gate) — no issues in 43 source files 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Overview** > Closes the remaining **Agent Skills security review** items with **documentation and tests only** — no runtime behavior changes beyond an expanded `safe_fs.py` module docstring. > > The **README** and **`agents.md`** now spell out deployment and platform limits: run **`write_skills` under a different identity than the agent** (with a shell check for agent writability), **decline a `ReconcileReport` root-writability field**, warn that **`"*"`** materializes the full skill library into context, and document the **POSIX-only** descriptor-pinned guarantee versus Windows’s racy `lstat` floor (reparse-point hardening explicitly deferred). > > **`test_skills_fs.py`** adds **`TestHostileManifestPrune`**: well-formed manifests that would prune `/etc/passwd`, traversal paths, or paths under a symlink-swapped parent must error without **`os.unlink`** being attempted (unlink spy), matching existing `_prune` defenses. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit 6a0e6aa. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).

…failure (Gap 2 / LA-2) (#58) ## Gap 2 (finding LA-2): a distinguishable outcome for integrity failure versus absence **This PR adds public API and needs review as such.** Three new exported names: `get_skill_result`, `SkillOutcome`, `SkillOutcomeReason`. ### The defect `get_skill` returns `None` for four distinct outcomes — no such skill, the store raised, the requested version is not the one held, and content that failed hash verification. A customer therefore cannot fail closed on suspected tampering while tolerating a merely-absent skill, so no automated customer-side response is possible. LA-1 (shipped in #51) gave the *operator* a structured log record; this gives the *application* the same distinction. The information already existed internally. `Resolution` in `skills_core.py` distinguished all four cases — but only as prose in its `error` string, which `get_skill` discarded with `.skill`. ### The API ```python SkillOutcomeReason = Literal["absent", "integrity_failure", "ok", "store_unavailable", "wrong_version"] @DataClass(frozen=True) class SkillOutcome: skill: Skill | None reason: SkillOutcomeReason detail: str | None async def get_skill_result(key: str, *, version: int | None = None) -> SkillOutcome: ... ``` Chosen over a typed exception, an opt-in strict mode, and an init-time callback. `detail` is the existing human-readable reason string — already safe to surface (skill key and failure mode only, never content, never a filesystem path), and a test pins that it stays that way. `get_skill_result` raises `RuntimeError` only when no store is configured, with the same message as `get_skill`. ### `get_skill` does not change Its contract — `None` for every failure, never raises for one — is documented in its docstring and in the README, and every existing caller treats `None` as "no skill". A test drives all four failures through both accessors: the reason is distinguishable *and* the collapsed form still collapses. ### Not matched on the error string `Resolution` grows a typed `reason`, set explicitly at every construction site. Deriving the public reason by pattern-matching `Resolution.error` is exactly the fragility LA-2 is about, so the mapping is a table a reviewer can read: | `resolve_from_store` outcome | `reason` | |---|---| | the store raised (`unavailable=True`) | `store_unavailable` | | `raw` is not a dict | `absent` | | `verify_raw_skill` returned `None` | `integrity_failure` | | `skill.version != wanted_version` | `wrong_version` | | success | `ok` | `reason` is declared **first and without a default**, so a contributor adding a sixth internal outcome has to decide which public token it maps to rather than inheriting one. That made the two `Resolution` sites in `skills_fs.py` explicit as well — both are the "could not retrieve" path, both already `unavailable=True`, both now say `reason="store_unavailable"`. `Resolution.unavailable` is unchanged. It stays load-bearing on the prune path — only a raising store suppresses pruning, because deleting managed files after a failed lookup would turn an outage into data loss — and `store_unavailable` stays distinct from `absent` for the same reason. ### Three things deliberately not built - **No new telemetry or log record.** Gap 1's `ld.skills.integrity_failure` record already fired inside verification before `resolve_from_store` returned. A test asserts one failed retrieval still produces exactly one log record and exactly one signal. - **Gap 1's 8-token `IntegrityReasonCode` is not threaded into `SkillOutcome`.** `verify_raw_skill` returns `None` and does not surface which token fired; plumbing it up would change that function's return type for a detail the operator already gets from the log record. The five-token public reason is the actionable surface. - **No batch equivalents.** `get_skills` and `all_skills` keep omitting failed entries and keep logging the run-level WARN count. A `get_skills_result` / `all_skills_result` would double the accessor surface for a case nobody has asked for — **possible follow-up** if a customer needs per-key reasons from a batch. ### Tests `packages/client/tests/test_skills.py`, one new class plus three additions to existing export/immutability tests: - one case per reason token — `reason`, whether `skill` is populated, non-empty `detail` - `store_unavailable` is distinct from `absent`: a raising store and an empty store - every non-`ok` outcome carries a detail (swept, so a fifth failure path with no message is caught by a test whose name says what it is about) - `get_skill` still returns `None`, and still never raises, for all four failures - `get_skill_result` raises `RuntimeError` with no store, asserted equal to `get_skill`'s message - no second integrity record or signal from `get_skill_result` - `detail` never carries the skill content - `SkillOutcome` is frozen; `SkillOutcomeReason`'s tokens and the three new exports are pinned ### Docs - `packages/client/README.md` — `get_skill_result` in the Agent Skills API table, a fail-closed example under the Gap 1 observability material (exit on `integrity_failure`, tolerate `absent`), the reason table, and an explicit statement that `get_skill` is unchanged and the two accessors differ only in what they report. - `packages/client/agents.md` — the five-token vocabulary, the `Resolution` → reason mapping, and the instruction that a sixth internal outcome must choose a public token rather than defaulting to `absent`. ### Lockstep with TypeScript The type name, the accessor name, and the five reason tokens are fixed across both SDKs; a sibling PR implements the identical shape in `typescript/`. Tokens are alphabetical, matching how `IntegrityReasonCode` was written on both sides in Gap 1. ### Placement Based on `split/skills-self-healing` (#57), which is based on #54. A new PR at the top of the stack so it disturbs none of the existing reviews: Gap 2 spans `types.py`, `skills.py`, `skills_core.py` and `__init__.py`, which #50–#53 own, and #52/#53/#54 are approved while #50/#51 have live reviewer conversation. ### Checks `uv run pytest` (1481 passed, 11 skipped), `ruff check`, `ruff format --check` all clean. `uv run mypy .` fails repo-wide on a pre-existing duplicate-`conftest` error before checking anything; scoped to the files this PR touches, mypy reports only two pre-existing `unused-ignore` warnings that are present on the base commit too. 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Overview** > Adds **`get_skill_result`** and frozen **`SkillOutcome`** / **`SkillOutcomeReason`** so applications can tell **integrity failure** apart from a missing skill, store outage, or version mismatch—without changing **`get_skill`** (`None` for all failures, same path, no extra telemetry). > > Internal **`Resolution`** now carries a required **`reason`** mapped explicitly at each **`resolve_from_store`** site (including **`skills_fs`** store-unavailable paths); **`get_skill_result`** exposes **`skill`**, **`reason`**, and safe-to-log **`detail`**. > > README and **`agents.md`** document fail-closed handling; tests cover all five reasons, immutability, exports, no double integrity signals, and unchanged **`get_skill`** behavior. > > Reviewed by [Cursor Bugbot](https://cursor.com/bugbot) for commit eda4ae1. Bugbot is set up for automated code reviews on this repo. Configure [here](https://www.cursor.com/dashboard/bugbot).

…esystem can hold (#57) Sixth PR in the Agent Skills stack, and the first that is not part of the original five-PR split. Implements **Gap 3 (AV-3)** and **Gap 4 (DV-2)** from the Agent Skills SDK security design review. Both live in `skills_fs.py`, so they ship together. Stack: #50 references → #51 retrieval → #52 safe-fs → #53 materialization → #54 fs-hardening → **#57 (this)**. ## Why this is a new PR rather than an edit to #53 The code Gap 3 changes lives in `skills_fs.py`, which #53 (`split/skills-materialization`) owns. Editing #53 would be the wrong move: - **#53 and #54 are `APPROVED`.** Editing #53 revokes that approval on the second-largest PR in the stack and forces #54 to rebase again — it has already been rebased twice this week (the str→bytes pivot, then the Gap 1 log record). - **Gap 3 relaxes a clobber refusal.** That is the most safety-sensitive change in the whole gap set, and it needs to be reviewable in isolation rather than buried in a rebase of an already-approved PR. Being a new branch on top, nothing below needs rebasing and no approval is disturbed. ## Gap 3 — self-healing partial reconciles (review priority: Medium) `_write_all` reconciles every skill and only then does `_rewrite_manifest` write the manifest, atomically, once, last. A process killed after a skill file lands but before that write leaves the file at a managed path with **no manifest entry** — exactly the condition `_write_one` treats as an unmanaged-file collision. The skill was then wedged permanently: every later reconcile took the same refusal branch. Boot-time execution under a ten-second budget makes the crash window realistic. `_write_one` now reads and hashes **first**, and decides from the bytes: ``` if exists: read on-disk bytes via _read_regular_file if sha256(on_disk) == content_hash -> adopt: record the entry, report skipped_current if not managed -> refuse, with the existing message else -> action = "updated" else: action = "written" ``` This cannot weaken the clobber guarantee, because only byte-identical LaunchDarkly content is ever adopted. Differing unmanaged bytes are still refused, untouched. **The existing clobber tests pass unchanged** — including `test_unmanaged_file_is_never_overwritten`, which writes `"user authored\n"`. Three details carry the safety: - **A failed read is a refusal, never an overwrite**, with a message distinguishable from the byte-mismatch refusal. It is the comparison that would otherwise authorize the write, and a file whose bytes could not be read has not been shown to be ours. - **The read stays on `_read_regular_file`, not `Path.read_bytes`.** Adoption widens it to genuinely foreign files, so its refusal of FIFOs and other non-regular files is now load-bearing rather than defensive. - **`skipped_current` is reused rather than adding an `adopted` kind**, so `ReconcileActionKind` in `types.py` — public, and owned by approved #50/#53 — does not change. Its documented meaning ("the bytes on disk already are the resolved content") already fits, and the reuse is documented in a comment. ### One decision the brief did not settle: a bound on the read Adoption reads files the manifest does not list, so `_read_regular_file` gained a `max_bytes` parameter and reads at most `len(content) + 1` bytes. Without it, adoption would be a memory amplifier: a multi-gigabyte file at a managed path would be slurped whole and then refused, where before the change it was refused without being read at all. The `+ 1` is load-bearing — a bound of exactly `len(content)` would adopt (and later prune) any customer file that merely *begins* with the resolved content. There is a test for that off-by-one, and it fails if the `+ 1` is removed. ### The caveat, stated plainly Adoption creates a manifest entry, so the adopted file becomes prunable on a later reconcile. That is correct and not a weakening: adoption only fires when the bytes are byte-identical to LaunchDarkly-resolved content, so a later prune removes content LaunchDarkly delivered anyway — exactly what would have happened had the crash not occurred. The guarantee that matters is preserved: **differing unmanaged bytes are never overwritten.** There is a test pinning the caveat too, so it cannot change silently. The review also floats a write-intent journal as an alternative. Assessed as over-engineered; **not built**. No case was found where the adoption rule fails. ## Gap 3, secondary — orphaned temp files (landed, not deferred) `atomic_write` names its temp file `.SKILL.md.<16 hex>.tmp` and unlinks it on exception — but not after a `SIGKILL`. `_prune` walks manifest entries, which an orphan never has, so nothing would ever notice one. The second-order effect is worse than the wasted bytes: `_prune_one`'s `rmdir` only succeeds on an empty directory, so **a single orphaned temp pins a skill's directory forever.** A sweep now runs on both the write and the prune path (before the `rmdir`, so it actually unblocks it). It is the one place this SDK removes a file the manifest does not list, so it is bounded on every axis: - inside `<root>/<key>/` only, for a key that passes `_key_rejection_reason`; - only names `safe_fs` itself recognizes — a new `is_temp_name` / `temp_name_prefix` pair beside the naming code, matched with `fullmatch` so both ends are anchored. The pattern is **derived from the producers rather than copied**: `atomic_write` and `_mkstemp_at` now build their names from the same constants the recognizer reads, and the recognizer covers both producers (`secrets.token_hex(8)` on the descriptor path, `tempfile.mkstemp`'s own sequence on the Windows fallback); - only regular files, with the type read off the descriptor, never a followed path; - unlinked through the existing descriptor-pinned `unlink_file` — no new path-based unlink; - never raises, never aborts a run; a failure is a logged warning. ## Gap 4 — Windows reserved device names (review priority: Low) The key grammar `^[a-z0-9][a-z0-9-]*$` admits `con`, `nul`, `aux`, `prn`, `com1`–`com9`, `lpt1`–`lpt9` — 22 names, none of which can be a directory name on Windows. Rejected in `_key_rejection_reason`, after `is_valid_skill_key`, matching the existing ordering discipline in that function. ### It belongs in the filesystem layer, not the shared key grammar `types_validation.skill_key_rejection_reason` / `is_valid_skill_key` are deliberately **untouched**. Please do not "correct" this: - `parse_ai_config` fails closed on a bad `skills` entry, by design. A grammar-level rejection would therefore invalidate the **entire AI Config** — model, provider, instructions, tools — for a Linux customer, over a constraint that only exists on Windows. - `skill_refs` would silently shrink, and its own docstring explains the consequence: a dropped reference lets `write_skills` **prune** the skill's on-disk copy. That converts "this skill fails to write on Windows" into "this skill gets deleted on Linux." - **Precedent:** the 255-byte component bound already lives in this layer for exactly this reason, documented in both codebases in those words. - `_key_rejection_reason` is already shared by the write and prune paths, so one edit covers both destructive paths. A test asserts the layer choice directly: for each of the 22 names, `is_valid_skill_key` is still `True`, `parse_ai_config` still accepts a config referencing it, and `skill_refs` still projects it. ### Unconditional, not platform-gated No `if os.name == "nt"`. - A managed root written by a Linux container can be read from a Windows host — an ordinary deployment — so the on-disk result must not depend on the writer's OS. - Neither repo has a Windows CI runner (verified: every job in `ci.yml` is `ubuntu-latest`), so a platform-gated branch would be untestable in CI — the exact condition that produced this gap. **The trade, stated honestly and belonging in the release notes:** a customer who legitimately names a skill `aux` now gets a reported `error` action on Linux where it would previously have worked. The set is exactly 22 names. No suffix stripping and no case folding are needed, and a comment says why: the key grammar admits no `.` and no `$`, so the `con.txt` and `CONIN$` / `CONOUT$` forms are unreachable, and keys are already lowercase-only. `com0` / `lpt0` are **not** reserved and are not included — there is a test for that, and for `con1` / `nul2` / `conx`. ### Residual documented, not implemented `MAX_PATH` overflow. The 255-byte bound is per *component* and does not bound the total path — `<customer root>` + `<key>` + `/SKILL.md` can still exceed Windows' 260-character `MAX_PATH` with a legal key. The SDK cannot validate this because the root is the customer's, so it is one README sentence rather than a check. ## Scope and non-goals - Neither gap emits the Gap 1 integrity-failure log record. A key rejection and a clobber refusal are `ReconcileAction` errors, not integrity failures — no `reason_code` tokens, no `record_integrity_failure` call. - No check in `_unsafe_path_reason`, `_key_rejection_reason`, or `safe_fs.py` was relaxed. `agents.md` marks these non-relaxable, and the new material there says the same about the adoption rule and the sweep, so a later contributor cannot widen either. - **No public API change**: `types.py` is untouched. - Gap 2 (typed outcome for integrity failure vs absence) is deliberately **not** here — it is a separate public-API decision, planned next. Gap 1 landed in #51 and was not modified. ## Docs - `packages/client/README.md`: the adoption rule under the existing `write_skills` conservatism paragraph, the reserved-name rejection with the honest trade, and the `MAX_PATH` residual. - `packages/client/agents.md`: the 22-name list, the adoption rule and its non-widenable details, the layer-choice reasoning, and the sweep's bounds — all in the non-relaxable-checks material. ## Tests `packages/client/tests/test_skills_fs.py`, +388 lines, 91 new cases: - **Crash-mid-reconcile recovery** (the review asks for this by name in the abuse suite): a byte-identical file with no manifest entry is adopted, reported `skipped_current`, recorded in the manifest, and the next reconcile is an ordinary no-op. Plus: adoption writes nothing (`os.replace` spy sees no call), emits `skipped_current` telemetry, and the adopted file is prunable afterwards. - Byte-differing unmanaged content still refused, untouched, no write attempted. - The `len + 1` off-by-one: a longer file sharing the content prefix is not adopted. - An unmanaged FIFO refused, not read, and does not hang. - A read error on an unmanaged file refuses rather than overwriting, with the distinguishable message, and adds no manifest entry. - Orphan swept on write; orphan no longer blocks `rmdir` on prune; eight lookalike names left alone; a symlink wearing the temp name is not removed and its target survives. - All 22 reserved names through **both** `write_skills` and the prune path, plus the grammar-level assertion above and the non-reserved neighbours. Every new test was mutation-checked — reverting each of the four behaviours (reserved-name check, sweep, adoption, the `+ 1`) makes the suite fail. ## Checks `uv run ruff format --check .`, `uv run ruff check .`, `uv run mypy packages/*/src` (CI's command), `uv run pytest` — all clean: **1469 passed, 11 skipped**. Note: `uv run mypy .` (the `Makefile`'s `typecheck` target) fails on a pre-existing duplicate-`conftest` module-resolution error in `packages/ai/tests` / `packages/claude-agents/tests`, unrelated to this change and present on `main`. CI runs `mypy packages/*/src`, which is clean. 🤖 Generated with [Claude Code](https://claude.com/claude-code)

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Cursor Bugbot has reviewed your changes using default effort and found 2 potential issues.

^{Reviewed by Cursor Bugbot for commit b62571e. Configure here.}

cursor · 2026-09-15T14:38:45Z

+            committed=True,
+            changes=changes,
+            basis=state if isinstance(state, str) and state else None,
+        )


Declined transfer advances delivery cursor

Medium Severity

A transfer declined as a foreign payload still returns committed=True and that payload's state as basis. _apply then overwrites the store cursor, so later reconnects request the wrong payload and skill updates, including revocations, stop arriving.

Additional Locations (1)

packages/client/src/launchdarkly_ai_server/skills_fdv2.py#L1556-L1558

^{Reviewed by Cursor Bugbot for commit b62571e. Configure here.}

cursor · 2026-09-15T14:38:45Z

+        if kind != SKILL_OBJECT_KIND:
+            return {}
+        with self._lock:
+            return self._objects.snapshot()


Unsynced store prunes on-disk skills

High Severity

get_object and all_objects return an empty snapshot without raising when no payload has committed, including after failed is set. write_skills and watch_skills treat that as an empty library rather than unavailable, so pruning deletes every managed SKILL.md.

Additional Locations (2)

packages/client/src/launchdarkly_ai_server/skills_watch.py#L308-L311

packages/client/src/launchdarkly_ai_server/skills_fs.py#L481-L496

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XieX mentioned this pull request Aug 25, 2026

feat(client): Agent Skills — umbrella for the #50–#54 split #45

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Comment thread packages/client/tests/test_skills_fs.py Outdated

XieX requested review from donei003 and knfreemLD August 26, 2026 20:11

donei003 approved these changes Aug 27, 2026

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knfreemLD approved these changes Aug 28, 2026

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XieX force-pushed the split/skills-materialization branch from b0d9e87 to 3709086 Compare August 28, 2026 18:03

XieX force-pushed the split/skills-fs-hardening branch from 13a851c to e87c5f9 Compare August 28, 2026 18:06

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Comment thread packages/client/tests/test_skills_fs.py

XieX and others added 2 commits August 28, 2026 16:12

XieX force-pushed the split/skills-fs-hardening branch from e87c5f9 to c88d5bf Compare August 28, 2026 20:29

XieX force-pushed the split/skills-materialization branch from 3709086 to 568729d Compare August 28, 2026 20:29

XieX mentioned this pull request Aug 30, 2026

feat(client): Agent Skills — self-healing reconciles, and keys no filesystem can hold #57

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XieX mentioned this pull request Aug 31, 2026

feat(client): Agent Skills — a distinguishable outcome for integrity failure (Gap 2 / LA-2) #58

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XieX and others added 11 commits September 4, 2026 10:19

XieX added 5 commits September 15, 2026 10:33

XieX merged commit ba215ef into split/skills-materialization Sep 15, 2026
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XieX deleted the split/skills-fs-hardening branch September 15, 2026 14:35

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test(client): Agent Skills — the filesystem abuse matrix (5/5) - #54

test(client): Agent Skills — the filesystem abuse matrix (5/5)#54
XieX merged 20 commits into
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Declined transfer advances delivery cursor

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Unsynced store prunes on-disk skills

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