Honor RUST_LOG in the Axum adapter logger

[dhruv8sh]

Summary

• The Axum dev server ignored RUST_LOG and always logged at trace, which floods stdout and writes full OpenRTB bid request bodies and TCF consent strings during routine local runs. It now reads the maximum level from RUST_LOG.
• When RUST_LOG is unset, the default is now info (matching the Fastly adapter) instead of trace. Nothing in the repo relies on Axum trace output: the integration harness discards Axum stdout, CI and scripts already set RUST_LOG=info, and the smoke script only checks error-level lines.
• Only a single level is supported (trace, debug, info, warn, error, off). Per-module filter syntax such as trace,hyper=info is not supported; it falls back to info and prints a startup warning to stderr.

Changes

File	Change
crates/trusted-server-adapter-axum/src/main.rs	Add resolve_max_level (parses RUST_LOG, defaults to info) and unrecognized_log_level (detects set-but-ignored values); pass the level to SimpleLogger::with_level; warn on stderr for unrecognized values; add unit tests for both helpers.
docs/guide/axum-dev.md	Add a Logging section covering the default level, supported values, the fallback warning, and the sensitivity of trace output.

The warning uses eprintln! only because the logger is not initialized yet at that point. This matches the existing PORT and logger-init warnings in main, which already sit under #[allow(clippy::print_stderr)].

Closes

Closes #1129

Test plan

• cargo test-fastly && cargo test-axum
• cargo clippy-fastly && cargo clippy-axum
• cargo fmt --all -- --check
• JS tests: cd crates/trusted-server-js/lib && npx vitest run
• JS format: cd crates/trusted-server-js/lib && npm run format
• Docs format: cd docs && npm run format
• WASM build: cargo build --package trusted-server-adapter-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve
• Other: cargo clippy-cloudflare && cargo clippy-cloudflare-wasm && cargo clippy-spin-native && cargo clippy-spin-wasm && cargo clippy-cli && cargo clippy-codegen, cargo test-cloudflare && cargo test-spin, and the parity test (cargo test --manifest-path crates/trusted-server-integration-tests/Cargo.toml --test parity)

Checklist

• Changes follow AGENTS.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses log macros (not println!); the startup eprintln! runs before the logger exists
• New code has tests
• No secrets or credentials committed

[ChristianPavilonis]

Review summary

Reviewed 0b149636304e0e7f184a9f3298f56f9b10d669a8 against cb945254521ed6dab365072f7caec10c524e323b. Both changed files were reviewed, including logger initialization, pinned dependency behavior, request handlers, and scripts consuming Axum output. No actionable issues introduced by this PR were found.

Safety proof

Runtime verification confirmed that the configured level controls actual output without changing HTTP behavior. A live-binary probe passed 12 cases covering every supported level, unset and blank values, whitespace and case normalization, and invalid filters. An actual EC trace record appeared only at trace; off suppressed all logs. Invalid filters warned on stderr. Every case retained /health HTTP 200 and malformed /auction HTTP 400.

Validation and review context

• cargo test-axum: 48 tests passed; one documentation example ignored.
• cargo fmt --all -- --check, cargo clippy-axum, and cargo build-axum: passed.
• In-memory Python live-binary logging matrix: all 12 cases passed after correcting a fixture rejected for known placeholder domains.
• cd docs && npm run format: blocked locally because prettier is unavailable. The CI docs check passed.
• All reported CI checks passed, including Axum tests, target-matched linting, docs formatting/build, parity, and integration tests.
• No existing reviews, inline comments, review threads, or PR issue comments were found.
• Residual risk: APS payload-specific trace output was not reproduced; the shared logging filter was verified through a real EC trace record.

The revision remained unchanged and the worktree stayed clean. No files were edited and no review work was delegated.

[prk-Jr]

Summary

The Axum logger now honors a single-level RUST_LOG setting and defaults to info. The startup warning, parser tests, and documentation agree with the selected behavior. No blocking or non-blocking findings.

Reviewed commit: 0b149636304e0e7f184a9f3298f56f9b10d669a8.

Validation

Read both changed files and compared the removed startup code, checked the pinned simple_logger and log implementations, and checked the EdgeZero startup path for competing logger initialization. Validation relies on GitHub CI; no local test suite was rerun.

CI Status

• integration tests: PASS
• browser integration tests: PASS
• integration tests (Fastly EC lifecycle): PASS
• CodeQL: PASS
• prepare integration artifacts: PASS
• cargo test (ts CLI, native): PASS
• format-typescript: PASS (required)
• cargo test (cross-adapter parity): PASS
• cargo check/build/test (spin native + wasm32-wasip1): PASS
• Analyze (rust): PASS
• format-docs: PASS (required)
• cargo test: PASS (required)
• vitest: PASS
• Analyze (actions): PASS
• cargo test (axum native): PASS
• cargo fmt: PASS (required)
• cargo check (cloudflare native + wasm32-unknown-unknown): PASS
• Analyze (javascript-typescript): PASS
• CLAUDE.md symlink guard: PASS
• Analyze (javascript-typescript): PASS