Tracer Code Review

Two-axis review of the diff between HEAD and a fixed point the user supplies:

• Standards — does the code conform to this repo's documented coding standards?
• Spec — does the code faithfully implement the originating issue / PRD / spec?

Both axes run as parallel sub-agents so they don't pollute each other's context, then this skill aggregates their findings. Each axis returns severity-graded findings and an explicit verdict — a review that only narrates is a review nobody can act on.

Process

1. Pin the fixed point

Whatever the user said is the fixed point — a commit SHA, branch name, tag, main, HEAD~5, etc. If they didn't specify one, ask for it. A workflow caller supplies its own fixed point and review budget.

Capture the diff command once: git diff <fixed-point>...HEAD (three-dot, so the comparison is against the merge-base). Also note the list of commits via git log <fixed-point>..HEAD --oneline.

Before going further, confirm the fixed point resolves (git rev-parse <fixed-point>) and the diff is non-empty. A bad ref or empty diff should fail here — not inside two parallel sub-agents.

2. Identify the spec source

Look for the originating spec, in this order:

1. A path or issue reference the caller passed as an argument.
2. Issue references in the commit messages (#123, Closes #45, etc.) — fetch via the tracker workflow in docs/agents/issue-tracker.md if it exists.
3. A PRD/spec file under docs/, specs/, or .tracer/ matching the branch name or feature.
4. If nothing is found, ask the user where the spec is. If they say there isn't one, the Spec sub-agent will skip and report "no spec available".

3. Identify the standards sources

Anything in the repo that documents how code should be written, such as CODING_STANDARDS.md or CONTRIBUTING.md.

On top of whatever the repo documents, the Standards axis always carries the smell baseline below — a fixed set of Fowler code smells (Refactoring, ch.3) that applies even when a repo documents nothing. Two rules bind it:

• The repo overrides. A documented repo standard always wins; where it endorses something the baseline would flag, suppress the smell.
• Always a judgement call. Each smell is a labelled heuristic ("possible Feature Envy"), never a hard violation — and, like any standard here, skip anything tooling already enforces.

Each smell reads what it is → how to fix; match it against the diff:

• Mysterious Name — a function, variable, or type whose name doesn't reveal what it does or holds. → rename it; if no honest name comes, the design's murky.
• Duplicated Code — the same logic shape appears in more than one hunk or file in the change. → extract the shared shape, call it from both.
• Feature Envy — a method that reaches into another object's data more than its own. → move the method onto the data it envies.
• Data Clumps — the same few fields or params keep travelling together (a type wanting to be born). → bundle them into one type, pass that.
• Primitive Obsession — a primitive or string standing in for a domain concept that deserves its own type. → give the concept its own small type.
• Repeated Switches — the same switch/if-cascade on the same type recurs across the change. → replace with polymorphism, or one map both sites share.
• Shotgun Surgery — one logical change forces scattered edits across many files in the diff. → gather what changes together into one module.
• Divergent Change — one file or module is edited for several unrelated reasons. → split so each module changes for one reason.
• Speculative Generality — abstraction, parameters, or hooks added for needs the spec doesn't have. → delete it; inline back until a real need shows.
• Message Chains — long a.b().c().d() navigation the caller shouldn't depend on. → hide the walk behind one method on the first object.
• Middle Man — a class or function that mostly just delegates onward. → cut it, call the real target direct.
• Refused Bequest — a subclass or implementer that ignores or overrides most of what it inherits. → drop the inheritance, use composition.

4. Spawn both sub-agents in parallel

Send a single message with two Agent tool calls and await both results. Use a fresh general-purpose sub-agent for each; Standards and Spec are rubrics, not configured agent types. Both prompts carry this preamble:

Verify, don't trust. Commit messages, code comments, and any implementer report are unverified claims — judge only the diff. Read-only review: never mutate the working tree, index, or HEAD.

Grade every finding: Critical (bugs, data loss, security, broken functionality), Important (can't be trusted until fixed — incorrect or fragile behavior, a missed requirement, swallowed errors, tests that assert nothing), or Minor (polish, style, "coverage could be broader"). Not everything is Critical. Every finding cites file:line and says why it matters. End with a verdict: Approved or Needs fixes (any Critical/Important finding means Needs fixes).

Standards sub-agent prompt — additionally include:

• The full diff command and commit list.
• The list of standards-source files you found in step 3, plus the smell baseline from step 3 pasted in full — the sub-agent has no other access to it.
• The brief: "Report — per file/hunk where relevant — (a) every place the diff violates a documented standard: cite the standard (file + the rule); and (b) any baseline smell you spot: name it and quote the hunk. Documented-standard breaches take the severity their impact earns; baseline smells are judgement calls and default to Minor unless the damage is concrete (e.g. verbatim duplication of a logic block is Important). A documented repo standard overrides the baseline. Skip anything tooling enforces."

Spec sub-agent prompt — additionally include:

• The diff command and commit list.
• The path or fetched contents of the spec.
• The brief: "Report: (a) Missing — requirements the spec asked for that are absent or partial; (b) Extra — behaviour in the diff that wasn't asked for (scope creep); (c) Misunderstood — requirements that look implemented but wrongly. Quote the spec line for each finding. A missing or misunderstood requirement is at least Important."

If the spec is missing, skip the Spec sub-agent and note this in the final report.

5. Aggregate

Present the two reports under ## Standards and ## Spec headings, each ending with its verdict. Do not merge or rerank findings — the two axes are deliberately separate (see Why two axes).

End with a one-line summary: verdict and finding counts per axis, and the worst issue within each axis (if any). Don't pick a single winner across axes — that's the reranking the separation exists to prevent.

6. Consuming the review

Workflow-owned review: return after step 5. The caller owns adjudication, repair, and the stopping rule. Any further review requires an assignment within its budget.

Standalone self-review: a review with confirmed open Critical/Important findings means the work is not done — reporting is not resolving. If you produced the diff and no enclosing workflow owns its repair budget:

1. Verify before implementing. Each finding is a claim — check it against the codebase. If a finding is wrong for this codebase (breaks existing behavior, misses context, violates YAGNI — grep for actual usage before "implementing properly"), push back with technical reasoning or put it to the user; don't blindly apply it. No performative agreement either way — evaluate, then fix or contest.
2. Fix in one pass. Dispatch one fix sub-agent (or fix inline) with the complete list of confirmed Critical/Important findings — never one fixer per finding. The fixer re-runs the covering tests and reports the output.
3. Re-review the failed axis on the updated diff. Loop until both axes are Approved.
4. Minor findings: fix cheaply now or record where the user will see them — never silently discard.

If the user asked for the review of someone else's changes, stop after step 5 — the report is the deliverable.

Why two axes

A change can pass one axis and fail the other:

• Code that follows every standard but implements the wrong thing → Standards pass, Spec fail.
• Code that does exactly what the issue asked but breaks the project's conventions → Spec pass, Standards fail.

Reporting them separately stops one axis from masking the other.