docs(agents): add non-obvious gotchas and bump go-colorable

AGENTS.md

@@ -6,12 +6,16 @@ Before opening a PR, run `make build && make test && make lint` (`make lint` mat
 ## Coding Style & Naming Conventions
 Prefer the standard library over new dependencies when possible. Keep tests in the same package unless black-box coverage is required.
 Repositories are processed in parallel, so every public `printer.Printer` method must hold `p.mu` while writing; cover new ones with a `*_ConcurrentSafe` test.
+Inside `syncer.execute`, `eg.Go` callbacks must always `return nil`: record per-repo failures in `runStats` (→ exit 2) and return `error` from `Run` only for setup failures (→ exit 1).
+This repo does not vendor dependencies; `make tidy` runs `go mod tidy` only — do not run `go mod vendor`.
 
 ## Testing Guidelines
 This repository uses Go’s `testing` package plus `github.com/matryer/is`. Write focused tests with `t.Run(...)`; avoid table-driven tests here. Use `t.Parallel()` whenever the case is safe to parallelize. Name receiver-related tests as `Test{Struct}_Xxx`, for example `TestSync_Execute`.
+Test `syncer` logic with `newSyncWithFake` (fake `Executor`) instead of spawning git. Real-git tests must be hermetic (bare repo under `t.TempDir()`, no network). Tests that swap `os.Stdout` cannot use `t.Parallel()`.
 
 ## Commit & Pull Request Guidelines
 Follow Conventional Commits with English titles, scoped by package when helpful, for example `feat(gih): ...`, `refactor(syncer): ...`, and `fix(printer): ...`. PRs should follow `.github/PULL_REQUEST_TEMPLATE.md` with `## Issue` and `## Overview`, link the related issue, and describe behavioral changes briefly in Japanese. Include tests for functional changes and update `README.md` when CLI behavior changes.
+Every push to `master` auto-tags a release (`.github/workflows/tagging.yml`). PRs are merge-committed, so each branch commit's type sets the bump: `fix` → patch, `feat` → minor, `BREAKING CHANGE:` footer → major, anything else → patch.
 
 ## Worktree Workflow
 Do not work directly on the default branch (currently `master`). Start each non-trivial change from a dedicated branch and worktree under `.worktrees/`, for example `git worktree add .worktrees/feat-x -b feat/x`.

go.mod

@@ -10,7 +10,7 @@ require (
 )
 
 require (
-	github.com/mattn/go-colorable v0.1.15 // indirect
+	github.com/mattn/go-colorable v0.1.16 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
 	golang.org/x/sys v0.48.0 // indirect
 )

go.sum

@@ -2,8 +2,8 @@ github.com/fatih/color v1.19.0 h1:Zp3PiM21/9Ld6FzSKyL5c/BULoe/ONr9KlbYVOfG8+w=
 github.com/fatih/color v1.19.0/go.mod h1:zNk67I0ZUT1bEGsSGyCZYZNrHuTkJJB+r6Q9VuMi0LE=
 github.com/matryer/is v1.4.0 h1:sosSmIWwkYITGrxZ25ULNDeKiMNzFSr4V/eqBQP0PeE=
 github.com/matryer/is v1.4.0/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
-github.com/mattn/go-colorable v0.1.15 h1:+u9SLTRGnXv73cEsnsmoZBom+dMU88B2M0aDcWy0/jY=
-github.com/mattn/go-colorable v0.1.15/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
+github.com/mattn/go-colorable v0.1.16 h1:+2YjeAe7xP1OQbZW1jERPWWCDLlNqFNCvjiqGiAt84A=
+github.com/mattn/go-colorable v0.1.16/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
 github.com/mattn/go-isatty v0.0.24 h1:tGZZoVgT/KiqK1c8ocVLeDS8BSWMRd47J3Lbz7vsReI=
 github.com/mattn/go-isatty v0.0.24/go.mod h1:nMCL3Zebbrt45jsMDgnfIwz6ydEQApk5oEI3HqDio6A=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=