feat(gptel-tools): wire git_status / git_log / git_diff as local tools

Three read-only git context tools so gptel can see what's changed
without me pasting `git status` / `git log` / `git diff` output into
every chat turn.  Builds the first batch from the ADOPT bucket in
`docs/design/gptel-tools-shortlist.org`.

Shape per tool:

- `gptel-tools/git_status.el` — `git status --short --branch` for a
  directory inside a git working tree under HOME.  Returns the
  porcelain output, or a "Clean working tree" marker when only the
  branch line is present.
- `gptel-tools/git_log.el` — `git log --oneline -nN` with an optional
  `--since` filter.  N defaults to 20, capped at 100; nil / non-
  integer / out-of-range N falls back to the default.
- `gptel-tools/git_diff.el` — `git diff [REF1 [REF2]] [-- FILE]`.
  Output capped at ~500KB so a runaway diff can't blow up context;
  truncation is reported inline.

Validation is uniform: path must resolve under HOME, must be a
directory, must be inside a git working tree (verified via
`git rev-parse --is-inside-work-tree`).  Color is disabled via
`-c color.ui=false` at the git level (`git status` doesn't accept
`--no-color` directly).

Tests run against real temp git repos created via `process-file`,
not mocked — there's nothing in gptel-tools/git_*.el that's
process-mockable in a meaningful way, and a real `git init` + a
couple of commits is cheaper than building a fake.  31 tests total:
7 for git_status, 11 for git_log, 13 for git_diff.

Wired into `cj/gptel-local-tool-features` so gptel exposes the
three tools on next restart.

1 files changed, 98 insertions, 0 deletions

diff --git a/tests/test-gptel-tools-git-status.el b/tests/test-gptel-tools-git-status.el
new file mode 100644
index 00000000..734abb31
--- /dev/null
+++ b/tests/test-gptel-tools-git-status.el
@@ -0,0 +1,98 @@
+;;; test-gptel-tools-git-status.el --- Tests for git_status gptel tool -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests run against real temp git repos under HOME via `process-file'.
+;; The tool is read-only so repos are torn down per test.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(eval-and-compile
+  (add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
+  (add-to-list 'load-path (expand-file-name "gptel-tools" user-emacs-directory))
+  (setq load-prefer-newer t)
+  (unless (featurep 'gptel)
+    (defvar gptel-tools nil)
+    (defun gptel-make-tool (&rest _args) nil)
+    (defun gptel-get-tool (&rest _args) nil)
+    (provide 'gptel)))
+
+(require 'git_status)
+
+;; ---------- helpers
+
+(defun test-gptel-tools-git-status--with-repo (fn)
+  "Create a temp git repo under HOME, call FN with its absolute path, clean up."
+  (let* ((name (format ".test-gptel-tools-git-status-%s"
+                       (format-time-string "%s%N")))
+         (dir (expand-file-name name "~")))
+    (unwind-protect
+        (progn
+          (make-directory dir)
+          (let ((default-directory dir))
+            (call-process "git" nil nil nil "init" "--quiet")
+            (call-process "git" nil nil nil "config" "user.email" "test@x")
+            (call-process "git" nil nil nil "config" "user.name" "Test")
+            (call-process "git" nil nil nil "commit" "--allow-empty"
+                          "--quiet" "-m" "initial"))
+          (funcall fn dir))
+      (when (file-exists-p dir) (delete-directory dir t)))))
+
+;; ---------- validate-path
+
+(ert-deftest test-gptel-tools-git-status-validate-path-normal ()
+  "Normal: validator accepts a directory inside a git working tree."
+  (test-gptel-tools-git-status--with-repo
+   (lambda (dir)
+     (should (equal (cj/gptel-git-status--validate-path dir) dir)))))
+
+(ert-deftest test-gptel-tools-git-status-validate-path-error-outside-home ()
+  "Error: path outside HOME signals."
+  (should-error (cj/gptel-git-status--validate-path "/etc")))
+
+(ert-deftest test-gptel-tools-git-status-validate-path-error-not-a-directory ()
+  "Error: path that's not a directory signals."
+  (let ((file (make-temp-file
+               (expand-file-name ".test-gptel-tools-git-status-" "~"))))
+    (unwind-protect
+        (should-error (cj/gptel-git-status--validate-path file))
+      (when (file-exists-p file) (delete-file file)))))
+
+(ert-deftest test-gptel-tools-git-status-validate-path-error-not-a-repo ()
+  "Error: directory outside any git working tree signals."
+  (let ((dir (make-temp-file
+              (expand-file-name ".test-gptel-tools-git-status-" "~") t)))
+    (unwind-protect
+        (should-error (cj/gptel-git-status--validate-path dir))
+      (when (file-exists-p dir) (delete-directory dir t)))))
+
+;; ---------- run
+
+(ert-deftest test-gptel-tools-git-status-run-clean-tree ()
+  "Normal: a clean repo returns the clean-tree marker."
+  (test-gptel-tools-git-status--with-repo
+   (lambda (dir)
+     (let ((out (cj/gptel-git-status--run dir)))
+       (should (string-match-p "Clean working tree" out))))))
+
+(ert-deftest test-gptel-tools-git-status-run-dirty-tree-includes-file ()
+  "Normal: an untracked file appears in the output."
+  (test-gptel-tools-git-status--with-repo
+   (lambda (dir)
+     (with-temp-file (expand-file-name "new.txt" dir) (insert "x"))
+     (let ((out (cj/gptel-git-status--run dir)))
+       (should (string-match-p "new.txt" out))
+       (should (string-match-p "^\\?\\?" out))))))
+
+(ert-deftest test-gptel-tools-git-status-run-includes-branch ()
+  "Normal: the `--branch' line surfaces in the output."
+  (test-gptel-tools-git-status--with-repo
+   (lambda (dir)
+     (with-temp-file (expand-file-name "f.txt" dir) (insert "x"))
+     (let ((out (cj/gptel-git-status--run dir)))
+       (should (string-match-p "^## " out))))))
+
+(provide 'test-gptel-tools-git-status)
+;;; test-gptel-tools-git-status.el ends here