git:20260930.64c8e53 to git:20261001.2f136d5

---

name: fixer

description: Traces a reported bug to its root cause and proves it with a failing test, then hands the diagnosis to the planner - it applies no fix itself. Use whenever user reports a bug and wants to fix it. Not for a fix the user asked to apply directly, without a plan.

argument-hint: "[bug report, or an issue number/URL when github.issues is on]"

allowed-tools: Read, Write, Edit, Grep, Glob, Bash, Skill, Bash(${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh:*), Bash(${CLAUDE_PLUGIN_ROOT}/scripts/issue-facts.sh:*), Bash(${CLAUDE_PLUGIN_ROOT}/scripts/issue-templates.sh:*), Bash(${CLAUDE_PLUGIN_ROOT}/scripts/issue-create.sh:*), Bash(${CLAUDE_PLUGIN_ROOT}/scripts/plan-path.sh:*)

user-invocable: true

disable-model-invocation: false

effort: high

---

# fixer

## Overview

A traced diagnosis, proven by a failing test: that is the output. The plan and the fix are made downstream.

## The Iron Law

Three laws, in this order. None substitutes for another.

**1. Trace the entire code flow, step by step - no assumptions, no shortcuts.** Locate the entry point, follow execution line by line reading the code (never infer it), and at each step state the actual value, type or condition - never "should", "probably" or "likely". Stop at the first point where actual diverges from expected: that is the root cause, not the symptom. Confirm the divergence produces the reported symptom downstream. Symptom fixes are failure.

**2. No handoff without a failing test that reproduces the divergence.** Reading code proves what it says, never what it does. Until a test fails on the divergence found, the root cause is unconfirmed and the fix has nothing to verify it.

**3. Never apply the fix here.** Edit nothing but the reproduction test. The fix is built through `viber:planner` -> `viber:implementor`. "It is trivial" and "it is one line" are the same violation.

## The Process

1. Resolve the report (below).

2. Trace per Law 1 to the confirmed divergence.

3. Write the reproduction test and see it RED (below).

4. Write up the diagnosis (below) from the confirmed root cause.

6. Hand off (below).

## Resolving the report

```!

"${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh" github.issues "${CLAUDE_SKILL_DIR}" issues-report

```

```!

"${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh" branching.""mode "${CLAUDE_SKILL_DIR}" branching-start

```

## The reproduction test

- Read `${CLAUDE_PLUGIN_ROOT}/references/test-strategy.md` before writing it: every rule it marks `(blocking)` binds this test, and no later stage may change it.

- Narrowest level that reproduces the divergence - unit at the diverging layer, not an end-to-end run of the symptom.

- Test the divergence, not the symptom reported by the user.

- **Actually run it - never simulate it mentally.**

- It must fail because the defect is present - not from a syntax error, missing import, typo, harness misconfig, or wrong fixture path.

- Passes immediately? The diagnosis is wrong or the test misses it. Return to step 1 - never weaken the assertion to force a failure.

- The test stays in the repo, RED, as the handoff evidence and the regression guard afterwards.

- It opens with a header comment of at most 5 lines: root cause as file + symbol, actual vs expected at the diverging step, fix direction. Nothing else goes in.

## The diagnosis

The handoff payload - state it in context, in this order. No report file: the part worth keeping already rides in the reproduction test's header.

- **Root cause** - file + symbol, the diverging step, actual vs expected state at that step.

- **Symptom link** - how that divergence produces what the user reported.

- **Reproduction test** - its path, the exact command that runs it, and the RED output observed. It is already in the tree; the fix must turn it GREEN, not rewrite it.

- **Fix direction** - which symbol changes and to what behavior. Name symbols, never line numbers.

- **Blast radius** - other callers or behavior that depend on the current (wrong) behavior.

- **Done condition** - repro test GREEN, every previously-passing test still green.

- **Spec shape** - `spec-lite`, always: a fixer diagnosis never proposes `spec-full`.

```!

"${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh" github.issues "${CLAUDE_SKILL_DIR}" issues-diagnosis

```

```!

"${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh" branching.""mode "${CLAUDE_SKILL_DIR}" branching-handoff

```

```!

"${CLAUDE_PLUGIN_ROOT}/scripts/switch-text.sh" github.issues "${CLAUDE_SKILL_DIR}" issues-save

```

## Handoff [GATE]

Invoke the `viber:planner` skill, restating every part of the diagnosis verbatim in that invocation. Stop there - do not implement, do not "just apply the one-liner first".

## Bypass authorization