Bug Hunting

Bug Hunting Workflow

Intent

This skill is for finding real bugs in the implementation, not guessing. It forces a discovery phase (build a mental model, reproduce, narrow scope) before making changes.

You must prioritize:

1. correctness and durability
2. clear reproduction
3. minimal fix + regression test

Non-negotiable rules

• No fix without a reproduction (a failing test, a minimal repro program, or a deterministic HTTP/CLI script).
• No durability regressions: do not weaken WAL/manifest/atomic rename/fsync ordering.
• No “drive-by refactors” while bug hunting; keep patches tight and reviewable.
• After changes, you must run the full quality suite from code-quality.

Discovery phase (required)

0) Establish the boundaries

Before opening files, answer (in notes) these questions:

• Which surface is affected? CLI, HTTP, embedded API, wasm, or ffi?
• Is it a correctness issue (wrong results), durability issue (lost/duplicated data), or stability issue (panic/hang)?
• Does it require a specific feature flag (vectors, zstd, gpu, wasm/IndexedDB, ffi)?
• Is the failure deterministic or intermittent?

1) Baseline the repo (don’t trust your local state)

Run in workspace root:

• cargo fmt --all
• cargo clippy --all --all-features --all-targets -- -D warnings
• cargo test --all --all-features

If anything fails here, you may be chasing a known failure; fix/resolve that first.

2) Map the architecture you’re about to debug

Create a quick map in notes (1–2 minutes):

• searchlite-core: schema, indexing, WAL/manifest, segments, query execution, filters/aggs, vectors
• searchlite-cli: user-facing commands and JSON output formatting
• searchlite-http: endpoints (/init, /add, /bulk, /delete, /commit, /refresh, /search, /inspect, /stats, /compact), limits/timeouts/concurrency
• searchlite-wasm: bindings + IndexedDB storage semantics (no fsync)
• searchlite-ffi: C ABI / safety edges

This map guides where you look first.

3) Reproduce the bug with the smallest possible corpus

Produce a “minimal reproducible case” artifact set:

• a schema JSON (small)
• a small NDJSON/doc list (5–50 docs)
• one request (HTTP JSON or CLI command) that fails

For HTTP:

• include the server flags/env (bind addr, index path, max-body-bytes, max-concurrency, request-timeout, refresh-on-commit)

For CLI:

• include exact commands and any flags

Goal: a script a teammate can run in <60 seconds.

4) Turn on observability (don’t add prints yet)

Use existing debugging features first:

• For search correctness: add explain: true to the request.
• For performance/odd slowdowns while reproducing: add profile: true.
• For server behavior: run with RUST_LOG=debug (or more targeted module filters) and capture the relevant lines.

If your issue is “writes not visible,” verify lifecycle:

• you must commit
• you may need /refresh in HTTP depending on config

5) Narrow the fault line by bisecting the pipeline

Pick one axis at a time:

Correctness axis

• Does the doc get ingested successfully?
• Does it appear in /stats documents?
• Does /inspect show a new segment after commit?
• Does the query match in bm25 mode vs wand/bmw mode?

Durability axis

• Is WAL appended correctly?
• Is manifest updated atomically?
• Is WAL truncated only after manifest persistence?
• After restart, does replay do the expected thing?

HTTP axis

• Is the request being rejected due to max body / timeouts / concurrency?
• Is NDJSON streaming partial and rolling back?
• Are errors correctly surfaced as {"error":{"type","reason"}}?

6) Perform a targeted static sweep of the suspected modules

Once you know the rough area, do a deliberate scan for bug smells:

Search patterns to grep/ripgrep for in the relevant crate:

• panics: unwrap(), expect(, panic!, unreachable!, todo!
• suspicious error handling: map_err(|_|, ok()? in non-optional contexts, silent let _ =
• integer edge cases: casts (as usize), underflow (- 1), unchecked indexing
• concurrency hazards: Mutex/RwLock lock ordering, .await while holding locks, channels without bounds
• IO hazards: missing fsync, non-atomic file replace, partial writes not handled, directory fsync omissions
• schema mismatch hazards: stringly-typed field lookups, analyzer lookup defaults, missing nested path validation
• vector hazards: dimension mismatch, normalization assumptions, unchecked candidate sizing, NaN propagation

You are not “fixing” in this step—just identifying suspects.

7) Dynamic bug probes by subsystem (choose what fits)

A) WAL / manifest / commit / rollback

If you suspect commit/durability issues:

• Reproduce a crash-window scenario:
  1. ingest docs
  2. start commit
  3. force termination mid-way (or simulate via test hooks if present)
  4. restart and observe replay
• Validate the invariants:
  • manifest atomic update (rename) and directory sync
  • WAL truncation happens after manifest sync
  • rollback cleans new segment artifacts

If you can’t safely crash in tests, create a unit test around writer/commit phases and validate state.

B) Segment lifecycle / compaction / cleanup

If you see duplicates, ghosts, or bloat:

• Inspect segments via inspect and compare to stats
• Run compaction and verify:
  • live docs preserved
  • deleted/tombstoned dropped
  • old segment files removed (or expected to remain until cleanup)

C) Query execution modes

If you suspect scoring/pruning bugs:

• Run the same query with execution=bm25, execution=wand, execution=bmw
• Results should match for deterministic corpora (unless the contract explicitly says otherwise)
• If they diverge, you likely have a pruning-bound bug or block-max metadata mismatch

D) Filters/aggs/nested correctness

If filters/aggs are wrong:

• Verify required fields are fast: true
• For nested, verify the filter uses a Nested block and that clauses bind to the same object instance
• Add a repro doc with two nested objects that would catch “cross-object” leakage

E) Vectors (feature vectors)

If vector behavior is wrong:

• Check dimension mismatch handling
• Check cosine normalization expectations
• Confirm ANN parameters (candidate_size, ef_search) don’t overflow or accept nonsensical values
• Verify hybrid search doesn’t double-count or drop vector scores

Fix phase (required)

1) Write the failing regression test first

• Prefer a unit test in the most local crate if possible.
• If the bug is surface-level behavior (HTTP contract, CLI output), add an integration test.
• Make it deterministic and small.
• Assert on structure, not strings (parse JSON output).

2) Implement the minimal fix

• Tight patch, minimal diff.
• Keep durability semantics intact.
• Avoid introducing allocations/locks in hot paths unless justified.

3) Prove it

Run:

• cargo test --all --all-features
• Any relevant examples (e.g. pruning example if you touched pruning logic)
• If the bug touched performance-sensitive code, run the relevant bench before/after.

4) Add a “root cause” note

In the PR description or internal notes, include:

• symptom
• root cause
• why the fix is correct
• what test prevents regressions

Output format (what Codex should produce)

When using this skill, produce:

1. Repro artifact (schema + docs + request/command)
2. Fault localization (files + functions involved)
3. Root cause analysis
4. Fix plan (minimal changes)
5. Regression test (where it lives and what it asserts)
6. Validation commands run (from code-quality)

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