feat(Phase4): add file changes for changestats executor wiring

Files changed: CLAUDE.md, internal/api/changestats.go,
internal/executor/executor.go, internal/executor/executor_test.go,
internal/task/changestats.go (new)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index 1d03678..16a48b4 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -105,6 +105,20 @@ Batch files wrap multiple tasks under a `tasks:` key.
 
 Two tables: `tasks` (with `config_json`, `retry_json`, `tags_json`, `depends_on_json` as JSON blobs) and `executions` (with paths to log files). Schema is auto-migrated on `storage.Open()`.
 
+## Features
+
+### Changestats
+
+After each task execution, Claudomator extracts git diff statistics from the execution's stdout log. If the log contains a git `diff --stat` summary line (e.g. `5 files changed, 127 insertions(+), 43 deletions(-)`), the stats are parsed and stored in the `executions.changestats_json` column via `storage.DB.UpdateExecutionChangestats`.
+
+**Extraction points:**
+- `internal/executor.Pool.handleRunResult` — calls `task.ParseChangestatFromFile(exec.StdoutPath)` after every execution; stores via `Store.UpdateExecutionChangestats`.
+- `internal/api.Server.processResult` — also extracts changestats when the API server processes a result (same file, idempotent second write).
+
+**Parser location:** `internal/task/changestats.go` — exported functions `ParseChangestatFromOutput` and `ParseChangestatFromFile` usable by any package without creating circular imports.
+
+**Frontend display:** `web/app.js` renders a `.changestats-badge` on COMPLETED/READY task cards and in execution history rows.
+
 ## ADRs
 
 See `docs/adr/001-language-and-architecture.md` for the Go + SQLite + WebSocket rationale.