docs(agents): sync code standards from vault Reference notes

[aliasunder]

Summary

• Initial distillation of vault Reference/code-standards-* notes into AGENTS.md's existing sections
• Fills gaps in ## Logging, ## Code style, ### Test conventions, and ## Operational docs — 100 insertions, zero deletions of existing repo-specific rules
• Adds provenance stamp for future staleness checks (<!-- distilled from vault ... on 2026-07-20 -->)

What changed, by section

Logging (5 rules from code-standards-logging-observability):
PII/credential ban, redaction via destructuring, catch-logs-or-rethrows, layer-appropriate error messages, internal-vs-external error detail separation

Code style (14 rules from code-standards-typescript):

• Error handling: per-operation try/catch, catch-logs-or-rethrows, explicit rejection over silent normalization
• Structure: extract multi-step callbacks, boolean mode param = split, block bodies for multiline, named params at >2 args, scope constants to usage site
• Comments: JSDoc on exports, durable rationale only, extraction preserves placement
• Types: TS 5.5 filter predicate inference, Boolean(x) over !!x
• Data-layer: no observability-only return values, prepared statements at factory scope

Test conventions (8 rules from code-standards-testing):
Two new two-bar traps (wrong-item pass, coincidental-equality hazard), never-decompose assertions, deterministic error messages get exact assertions, cleanup via onTestFinished, test-per-module structure, separate it() over callback it.each, error-path coverage, never mock time internals, production type rules in tests

Operational docs (6 rules from code-standards-docs):
Reader-walk persona test, multi-path doc coverage, structural self-references as claims, sibling-doc coherence, factual-claims-match-code, mechanism language earned

Promotion pass: no candidates — existing repo-specific rules are either already covered by the Reference notes or too project-specific (MCP conventions) to generalize.

Test plan

• Docs-only change — no code affected
• Pre-commit hooks pass (tsc + lint-staged + prettier)
• All additions are gap-fills; no existing rules modified or deleted
• Provenance stamp enables future staleness checks

🤖 Generated with Claude Code

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