docs: document timestamp column units (epoch ms) in ARCHITECTURE.md and fresh-install schema

[G0-0000]

Follow-up to #457, reshaped per maintainer feedback (magic-alfonso).

Changes

ARCHITECTURE.md — added a ### Timestamp Columns table in the storage section listing each created_at/updated_at column with its unit (epoch ms) and the writer that stamps it. Every row was verified against its writer; columns with mixed writers (memories host/Rust-mirror) or non-TypeScript writers (workspaces, dashboard Rust) are called out explicitly rather than blanket-asserted.

packages/plugin/src/features/magic-context/storage-db.ts — adds -- epoch ms (Date.now()) comments to created_at columns in the fresh-install schema only (no migration DDL touched — shipped migrations stay append-only). Only columns verified to be stamped by Date.now() get the comment; memories/workspaces are deliberately omitted.

No behavior change. Not touching migrations.ts per the maintainer's "applied migrations are history" note.

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Summary by cubic

Documents the audited timestamp columns as epoch milliseconds in ARCHITECTURE.md and annotates verified fresh-install schema columns with their Date.now() units. Clarifies timestamp handling without changing runtime behavior or migration history.

• The architecture table lists each column's writer and flags caller-supplied overrides (row.createdAt, candidate.createdAt, input.now, refreshedAt), clone-preserved timestamps, and mixed (memories) or Rust (workspaces) writers.
• Schema comments appear only where Date.now() is the actual writer.
• Shipped migrations are unchanged, so existing databases need no migration step.

^{Written for commit 8d76de6. Summary will update on new commits.}

Greptile Summary

Documents the units and provenance of audited timestamp columns without changing runtime behavior or migration history.

• Adds an architecture table covering epoch-millisecond timestamp writers, caller overrides, clone preservation, schema defaults, and mixed TypeScript/Rust writers.
• Annotates verified fresh-install schema columns with timestamp-unit comments.
• Clarifies that primer answer refreshes may supply refreshedAt.

Confidence Score: 5/5

The PR appears safe to merge because it only clarifies timestamp documentation and schema comments, with no outstanding correctness or repository-rule issues.

The prior timestamp-provenance concern was addressed and its thread is resolved; the subsequent refreshedAt clarification accurately documents the remaining caller-supplied path.

Important Files Changed

Filename	Overview
ARCHITECTURE.md	Adds an audited timestamp-unit and writer-provenance reference, including explicit override and preservation paths.
packages/plugin/src/features/magic-context/storage-db.ts	Adds comments to fresh-install schema declarations without altering SQL semantics or migration history.

_{Reviews (3): Last reviewed commit: "docs: note refreshedAt override on prime..." | Re-trigger Greptile}

[cubic-dev-ai]

All reported issues were addressed across 2 files

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 2 files (changes from recent commits).

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[magic-alfonso]

Merged as-is — the per-writer verified table is exactly what #457's decline asked for, the memories mixed-writer note checks out against master (placeholder allocated at 0, then the module snapshot's own timestamps applied), and the fresh-install DDL comments touch no applied migration. Storage suite green on the head. One note: ARCHITECTURE.md is periodically regenerated by our docs task, which may reflow this section; the content survives that, the exact layout may not. Thanks for the quick reshaping.