Hunt: Diagnose Before You Fix

Prefix your first line with 🥷 inline, not as its own paragraph.

A patch applied to a symptom creates a new bug somewhere else.

Do not touch code until you can state the root cause in one sentence:

"I believe the root cause is [X] because [evidence]."

Name a specific file, function, line, or condition. "A state management issue" is not testable. "Stale cache in useUser at src/hooks/user.ts:42 because the dependency array is missing userId" is testable. If you cannot be that specific, you do not have a hypothesis yet.

Diagnosis Signals

Good progress: a log line matches the hypothesis, you can predict the next error before running it, you understand the propagation path from root cause to symptom, you can write a test that fails on the old code. At each of these signals, find one more independent piece of evidence before committing.

Hypothesis quality gate: before acting on a hypothesis, list all observable symptoms (not just the one the user reported first). The hypothesis must explain every symptom; if it only covers some, it is a symptom-level guess, not a root cause. For timing-dependent issues (flicker, intermittent failure, race condition), reproduce reliably before diagnosing.

Rationalization warning: "I'll just try this" means no hypothesis, write it first. "I'm confident" means run an instrument that proves it. "Probably the same issue" means re-read the execution path from scratch. "It works on my machine" means enumerate every env difference before dismissing. "One more restart" means read the last error verbatim; never restart more than twice without new evidence.

Hard Rules

• Same symptom after a fix is a hard stop; so is "let me just try this." Both mean the hypothesis is unfinished. Re-read the execution path from scratch before touching code again.
• After three failed hypotheses, stop. Use the Handoff format below to surface what was checked, what was ruled out, and what is unknown. Ask how to proceed.
• Verify before claiming. Never state versions, function names, or file locations from memory. Run sw_vers / node --version / grep first. No results = re-examine the path.
• External tool failure: diagnose before switching. When an MCP tool or API fails, determine why first (server running? API key valid? Config correct?) before trying an alternative.
• Pay attention to deflection. When someone says "that part doesn't matter," treat it as a signal. The area someone avoids examining is often where the problem lives.
• Visual/rendering bugs: static analysis first. Trace paint layers, stacking contexts, and layer order in DevTools before adding console.log or visual debug overlays. Logs cannot capture what the compositor does. Only add instrumentation after static analysis fails.
• Fix the cause, not the symptom. If the fix touches more than 5 files, pause and confirm scope with the user.

Bisect Mode

Activate when: "以前是好的", "之前是好的", "used to work", "上一次提交还是对的", "broke after update", or the user remembers a specific good commit or version.

1. Find candidate good tag: git tag --sort=-version:refname | head -10 or ask the user for the last known-good commit.
2. Define a non-interactive pass/fail test command before starting bisect. Bisect is worthless without a reproducible check.
3. Run: git bisect start && git bisect bad HEAD && git bisect good <tag-or-hash>
4. At each step bisect checks out a commit. Run the test command. Mark: git bisect good or git bisect bad.
5. Let bisect drive. Do not jump ahead or skip commits unless explicitly asked.
6. When bisect names the culprit commit, read only that diff. Identify the specific line that introduced the regression.
7. Run git bisect reset when done.

Read large files once and reference from notes rather than re-reading at each bisect step.

Repeated Regression / Screenshot Reference Mode

Activate when the user says the same issue is still wrong after a fix, provides a "good" screenshot/version/file, or describes a visual result as previously correct.

Treat the reference as evidence, not decoration:

1. List every reported and visible symptom, preserving the user's concrete words where useful ("still slow", "not clear", "尖刺", "先显示上一个内容").
2. Identify the reference oracle: last-good commit/tag, old build, fixture, screenshot, downloaded artifact, or expected state from the user's description.
3. Define the pass/fail check before editing. For visual bugs, this may be a narrow screenshot checklist plus the command that renders the view; for behavioral bugs, prefer an automated regression test or deterministic repro.
4. Compare current vs. reference and name the exact delta. Do not generalize a visual defect into "style polish" when the evidence points to a broken render, race, font pipeline, or state path.
5. If the same symptom remains after one attempted fix, stop and rebuild the hypothesis from the evidence. Do not stack more patches onto a disproven explanation.

If the issue is purely subjective UI taste, route to /design. If it is rendering, state, timing, build output, font generation, or a regression from a known-good version, stay in /hunt.

Confirm or Discard

Add one targeted instrument: a log line, a failing assertion, or the smallest test that would fail if the hypothesis is correct. Run it. If the evidence contradicts the hypothesis, discard it completely and re-orient with what was just learned. Do not preserve a hypothesis the evidence disproves.

Targeted Logging

Use logs as a scalpel, not as noise. Before adding a log, write the question it answers:

"If this log prints X before Y, hypothesis A is still possible; if it does not, hypothesis A is wrong."

Load references/logging-techniques.md for the full logging playbook: binary-search instrumentation, discriminating log content, boundary-first placement, timing bug logging, and removal discipline.

Quick rules:

1. Place the first log at the midpoint of the execution path, not at the symptom. Binary search from there.
2. Log discriminating facts only: sequence number, input key, branch taken, old/new state, error code.
3. Remove temporary logs before finishing. Gate persistent diagnostics behind the project's debug flag.

If adding logs changes the behavior, treat that as evidence of a timing, lifecycle, or concurrency problem.

Gotchas

Outcome

Success Format

Root cause:        [what was wrong, file:line]
Fix:               [what changed, file:line]
Confirmed:         [evidence or test that proves the fix]
Tests:             [pass/fail count, regression test location]
Regression guard:  [test file:line] or [none, reason]

Status: resolved, resolved with caveats (state them), or blocked (state what is unknown).

Regression guard rule: for any bug that recurred or was previously "fixed", the fix is not done until:

1. A regression test exists that fails on the unfixed code and passes on the fixed code.
2. The test lives in the project's test suite, not a temporary file.
3. The commit message states why the bug recurred and why this fix prevents it.

Handoff Format (after 3 failed hypotheses)

Symptom:
[Original error description, one sentence]

Hypotheses Tested:
1. [Hypothesis 1] → [Test method] → [Result: ruled out because...]
2. [Hypothesis 2] → [Test method] → [Result: ruled out because...]
3. [Hypothesis 3] → [Test method] → [Result: ruled out because...]

Evidence Collected:
- [Log snippets / stack traces / file content]
- [Reproduction steps]
- [Environment info: versions, config, runtime]

Ruled Out:
- [Root causes that have been eliminated]

Unknowns:
- [What is still unclear]
- [What information is missing]

Suggested Next Steps:
1. [Next investigation direction]
2. [External tools or permissions that may be needed]
3. [Additional context the user should provide]

Status: blocked

Rendering Bug Mode

Activate when: "PDF looks wrong", "page break issue", "font not rendering", broken PDF output, or print layout wrong.

Load references/rendering-debug.md for the full diagnosis checklist (WeasyPrint quirks, font loading, page overflow, browser print CSS). Static analysis first, then reproduce if needed.

IME / Unicode Issues

For input method, character rendering, or text encoding bugs (IME state, cursor drift, emoji splitting, composition events), check references/ime-unicode.md first before forming a hypothesis.