chore: import upstream snapshot with attribution

plugin/skills/commit-context/EXAMPLES.md

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+# commit-context worked examples
+
+## 1. Line range with a linked session
+
+User: "Why is this retry loop here?" (pointing at lines 40-52 of refresh.ts)
+
+Find the SHA:
+
+```bash
+git blame -L 40,52 src/auth/refresh.ts
+# 9a1b2c3d (dev 2026-06-07) ... retry on revoked token
+```
+
+Look it up:
+
+```json
+memory_commit_lookup { "sha": "9a1b2c3d4e5f60718293a4b5c6d7e8f901234567" }
+```
+
+Response:
+
+```json
+{
+  "commit": { "sha": "9a1b2c3d...", "short": "9a1b2c3", "branch": "main",
+    "author": "dev", "message": "rotate refresh tokens" },
+  "sessions": [ { "id": "7f3a9c21", "project": "app", "observationCount": 14,
+    "summary": "Reworked refresh rotation" } ]
+}
+```
+
+Present:
+
+> `9a1b2c3` on `main` by dev: "rotate refresh tokens". Linked to session
+> `7f3a9c2` "Auth refresh rework" (14 obs). The retry loop handles a token
+> revoked mid-flight, per the session's high-importance observations.
+
+## 2. Function lookup, commit predates linking
+
+User: "What was the agent doing when it wrote validateScope?"
+
+```bash
+git log -L :validateScope:src/auth/scope.ts -n 1
+# 1122aabb ...
+```
+
+```json
+memory_commit_lookup { "sha": "1122aabbccddeeff00112233445566778899aabb" }
+```
+
+Response:
+
+```json
+{ "commit": null }
+```
+
+Present:
+
+> `1122aab` predates agent session linking, so there is no recorded session.
+> From `git show`: it added `validateScope` to enforce per-token scopes. I can
+> show the full diff if useful.
+
+## 3. Bare path
+
+User: "Give me context on src/middleware/limit.ts."
+
+```bash
+git log -n 1 -- src/middleware/limit.ts
+```
+
+Take the SHA, run `memory_commit_lookup`, present commit plus linked session in
+the same shape as example 1.

plugin/skills/commit-context/SKILL.md

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+---
+name: commit-context
+description: Trace a file, function, or line back to the agent session that produced its current commit. Use when the user asks "why is this code here", "what was the agent doing when this changed", "who wrote this", or wants context on a specific location in the codebase.
+argument-hint: "[file, function, or line]"
+user-invocable: true
+---
+
+The user wants commit context for: $ARGUMENTS
+
+## Quick start
+
+```bash
+git blame -L 40,52 src/auth/refresh.ts   # -> SHA 9a1b2c3d
+```
+
+```json
+memory_commit_lookup { "sha": "9a1b2c3d4e5f60718293a4b5c6d7e8f901234567" }
+```
+
+Expected output:
+
+```text
+9a1b2c3 on main by dev: "rotate refresh tokens"
+Linked session 7f3a9c2 "Auth refresh rework", 14 obs.
+```
+
+## Why
+
+Report only what git and the lookup return. When the lookup gives `commit: null`,
+the commit predates session linking; do not invent intent.
+
+## Workflow
+
+1. Find the SHA: `git blame -L <start>,<end> <file>` for a line range;
+   `git log -L :<function>:<file>` for a function; `git log -n 1 -- <file>` for a
+   bare path.
+2. Look it up: `memory_commit_lookup { "sha": "<full-sha>" }`.
+3. Present the commit (sha, short sha, branch, author, message), the linked
+   session(s) (id, project, started/ended, observation count, summary), and the
+   importance >= 7 observations via `memory_recall` when available.
+
+## Anti-patterns
+
+WRONG: lookup returns `{ "commit": null }`, you narrate "the agent was
+refactoring auth" from the diff alone.
+
+RIGHT: "This commit predates session linking, so there is no recorded agent
+session. From `git show`: it changed token rotation in refresh.ts."
+
+## Checklist
+
+- SHA came from git blame/log, not a guess.
+- `commit: null` reported as "predates linking", no fabricated session.
+- Session details quote the lookup response verbatim.
+- No intent claimed beyond what observations state.
+
+## See also
+
+- `commit-history`: list many agent-linked commits at once.
+- `recall`: dig deeper into the linked session's observations.
+
+## Troubleshooting
+
+See ../_shared/TROUBLESHOOTING.md if `memory_commit_lookup` is not available.