feat(parquet): add a durable audit sink over the §3.7 Parquet stream

[jensholdgaard]

What

A durable ParquetAuditSink (AuditSink) that persists audit events to the RFC 0005 §3.7 audit Parquet stream — the concrete sink the ourios-server binary will hand the compactor (chosen over a NoOp placeholder so compaction audit events actually land on disk).

Design

• emit(event) derives the event's audit partition (tenant + UTC day, RFC 0005 §3.4) and writes a single-event file (audit/tenant_id=…/year=…/month=…/day=…/<uuid>.parquet) via AuditWriter.
• Infallible emit (the AuditSink contract) → write failures bump a write_failures counter rather than propagating, surfaced there until the logging/metrics bootstrap (CLAUDE.md §6.3).
• File-per-event is acceptable for the low-volume compaction audit stream (≤ one event per compacted partition per sweep). Batching + the §6.4 crash-ordering barrier come with the WAL-backed sink (RFC 0005 §3.7 / RFC 0008), which supersedes this best-effort pre-WAL persistence — and the §6.4 barrier is moot for compaction (it commits before its audit event).

RFC note

RFC 0005 §3.7 routes durable+ordered audit through the WAL (post-MVP). This sink provides best-effort persistence using the already-specified §3.7 format in the meantime — strictly better than the "in-memory until the WAL" status quo, without changing the format the WAL path will also write.

Test

Emit a compaction event → read it back byte-for-byte from its derived audit partition via AuditReader.

Verification

cargo fmt --all --check, cargo clippy --all-targets --all-features -D warnings, cargo test -p ourios-parquet --all-features — all green.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added persistent audit event storage in Parquet format for durable recording to a configured location.
  • Write failures are handled gracefully with internal tracking, ensuring operations continue reliably without interruption.

[jensholdgaard]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 4f303db6-598b-4dc2-9075-7686566b3d52

📥 Commits

Reviewing files that changed from the base of the PR and between f77767c and 637ad51.

📒 Files selected for processing (2)

• crates/ourios-parquet/src/audit_sink.rs
• crates/ourios-parquet/src/lib.rs

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📝 Walkthrough

Walkthrough

This PR adds ParquetAuditSink, a new trait implementation for durable audit event persistence. Each audit event is written as a single-event Parquet file in an RFC 0005 audit partition layout. Write failures are handled gracefully via saturating counter increments rather than error propagation. The new sink is tested end-to-end and exposed via the crate's public API.

Changes

Audit Event Persistence to Parquet

Layer / File(s)	Summary
ParquetAuditSink struct and persistence logic crates/ourios-parquet/src/audit_sink.rs	ParquetAuditSink struct holds bucket_root and a write_failures saturating counter. Constructor and write_failures() accessor provide initialization and monitoring. try_write() helper derives the audit partition from the event and uses AuditWriter to open, append the single event, and close. AuditSink::emit trait implementation calls try_write() and increments the counter on error without propagating.
Audit event persistence integration test crates/ourios-parquet/src/audit_sink.rs	Test creates a temporary bucket, emits a fixed compaction audit event, verifies write_failures remains zero, derives the expected partition path, locates the single written .parquet file, reads all events back via AuditReader, and asserts byte-for-byte equality with the original event.
Public API module and re-export crates/ourios-parquet/src/lib.rs	New audit_sink module declaration and ParquetAuditSink re-export extend the crate's public API surface for audit sink functionality.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• jensholdgaard/ourios#110: The main PR's new ParquetAuditSink implements the same AuditSink trait that this PR's Compactor uses to emit per-compaction AuditEvents, so the two changes are directly connected in the audit-event persistence/emission flow.
• jensholdgaard/ourios#46: Main PR's new ParquetAuditSink writes each AuditEvent by opening/append/closing Parquet via the AuditWriter/partition layout introduced in this PR, tying the sink directly into that audit writer/reader codepath.

Poem

🐰 A Parquet sink hops forth so fine,
Each audit event in its rightful line,
Failures count up, but never break the flow,
Persistence blooms where audit events go! 🌱

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: adding a durable audit sink implementation over the RFC 0005 §3.7 Parquet stream format.
Description check	✅ Passed	The pull request description is comprehensive and well-structured, covering the what, design rationale, RFC context, testing approach, and verification steps performed.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/parquet-audit-sink

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[jensholdgaard]

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