git-history-diagnostic

A troubleshooting workflow for finding the change that caused a previously working behavior to break. It compares versions in a Git history, which records how the code changed over time.

In plain words
What is it for?
It helps investigate regressions by comparing a known-good version with the broken version or narrowing the cause through Git history.
Why use it?
It avoids guessing at the fix by locating the commit—the saved set of code changes—where the regression entered.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/fusebase-dev/fusebase-flow/git-history-diagnostic
Any agent
npx skills add fusebase-dev/fusebase-flow --skill git-history-diagnostic
Clone the repo
git clone --depth 1 https://github.com/fusebase-dev/fusebase-flow

Made for: Claude Code, Codex.

Per session 100 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,550 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00100 $0.01550
Opus 5 $0.00050 $0.00775
Sonnet 5 $0.00020 $0.00310
Haiku 4.5 $0.00010 $0.00155

Measured 2d ago against content hash c6d7cb33a4c6, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

git-history-diagnostic scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.agents/skills/git-history-diagnostic/SKILL.md · 115 lines

How it starts

The opening of the file, as written. The whole thing — 115 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Git History Diagnostic

Style: Mode-B-lite.

Purpose

Regression archaeology: when behavior that previously worked is now broken, locate where it broke by comparing commits / bisecting history — so the fix targets the actual causing change, not a guess. Read-only diagnosis; the fix is handed to zoom-out + validation-and-qa.

When to invoke

  • "It used to work" / "this is a regression" / "when did X break".
  • A test that passed at an earlier commit now fails.
  • Operator points to a known-good prior state and a now-broken current state.

Do not invoke when

  • The behavior never worked (net-new bug → normal debugging).
  • Routine rollback of a known commit → workflows/git-discipline.md.
  • Reproduction isn't established yet → run FR-10 reproduce-before-fix first (you need a reliable signal to bisect against).

Required inputs

Input Where it lives If missing
A reliable broken/works signal (test or repro) test suite / repro steps establish via FR-10 first; bisecting needs a yes/no test
Last-known-good reference (commit/tag/date) operator / git history search backward from HEAD for the transition
Current broken state HEAD

Procedure

  1. Pin the signal. Define a deterministic check that returns good/bad (a test command, a repro). Bisection is only as reliable as this signal.
  2. Bracket. Identify a known-good commit (or tag/date) and a known-bad commit (usually HEAD). Verify the signal at both ends.
  3. Bisect. Narrow the range with git bisect run on the pinned signal (see § Bisect mechanics; manual good/bad stepping or binary search when the signal is not scriptable) until the first bad commit is found.
  4. Explain. Show that commit's diff; identify the specific change that introduced the regression (file:line).
  5. Hand off. Pass the finding to zoom-out (root-cause vs revert decision) and validation-and-qa for the fix + regression test. Do not fix here.
  6. Capture. If the regression class is recurring, note it in docs/problem-catalog/.

Read the full file on GitHub · 115 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 115 lines · 100 tokens per session scan A c6d7cb33a4c6

Subscribe to this mod's changes

git-history-diagnostic is a skill published in the GitHub repository fusebase-dev/fusebase-flow (9 stars, last pushed 7d ago), licensed MIT. It adds 100 tokens to every session and 1,550 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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