feat(dev-fkeys): revert projectile cache on failed-and-modified compile

Without this, a one-off typo at projectile's compile/test/run prompt poisons the per-project cache: every subsequent invocation pre-fills the broken value. I hit it during the Phase 2a live-test, where projectile's "All tests" prompt was replaying `go test ../.` and there was no clean way to get the prior known-good back.

Three pieces of machinery, all in `dev-fkeys.el`:

`cj/--projectile-capture-cmd' captures the current cached cmd at the project root before each invocation, stashing a plist with :map / :root / :prior in `cj/--projectile-revert-state'.

`cj/--projectile-revert-on-fail' is a `compilation-finish-functions' hook that reads that state. If the compile failed AND the cmd was modified from the captured prior value AND the prior was non-nil, it puts the prior back in projectile's cmd-map. Test-fails-because-of-real-bug (cmd unchanged through the run) leaves the cache alone. The hook self-removes on first invocation regardless of outcome and clears the state.

`cj/--projectile-around-revert' is the around-advice that wires the two together. I added the advice to all three projectile cmd-runners — `projectile-compile-project', `projectile-test-project', `projectile-run-project' — so the auto-revert applies whether the user invoked via F4 / F6 or directly via `M-x'.

Plus the manual escape-hatch: `cj/projectile-reset-cmds' clears compile/test/run cache for the current project. Bound to `C-; P' under the personal keymap. Use when projectile's auto-derived default was wrong from the start and you want to start fresh — the next F4 / F6 invocation re-derives projectile's project-type default.

TDD: 18 new tests across 4 files, one per helper. The around-advice tests build the capture/install/orig-fn flow against stub cmd-maps and verify state captured, hook installed, orig-fn invoked. The revert hook tests cover failure-and-modified (revert), success (leave alone), failure-but-unchanged (leave alone), nil prior (leave alone), nil state (no-op), and self-removal. The reset-cmds tests cover the all-three-maps clear, no-cached-entry no-op, and no-project user-error.

1 files changed, 70 insertions, 0 deletions

diff --git a/tests/test-dev-fkeys--projectile-capture-cmd.el b/tests/test-dev-fkeys--projectile-capture-cmd.el
new file mode 100644
index 00000000..92309198
--- /dev/null
+++ b/tests/test-dev-fkeys--projectile-capture-cmd.el
@@ -0,0 +1,70 @@
+;;; test-dev-fkeys--projectile-capture-cmd.el --- Tests for cj/--projectile-capture-cmd -*- lexical-binding: t -*-
+
+;;; Commentary:
+;; Tests for the prior-cmd capture helper used by the auto-revert advice.
+;; Captures the current cached cmd at the project root into
+;; `cj/--projectile-revert-state' so a later finish-hook can restore it
+;; if the compile fails after the cmd was modified.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'dev-fkeys)
+
+;; Test stub: projectile cmd-maps as defvars so `boundp' is non-nil and
+;; `let'-binding has a target. In real use, projectile defines these.
+(defvar projectile-compile-cmd-map nil)
+(defvar projectile-test-cmd-map nil)
+(defvar projectile-run-cmd-map nil)
+
+;;; Normal Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-stores-prior-value ()
+  "Normal: captures the cached cmd at the project root into the state plist."
+  (let* ((cj/--projectile-revert-state nil)
+         (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (puthash "/p/" "make build" projectile-compile-cmd-map)
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-capture-cmd 'projectile-compile-cmd-map))
+    (should (equal (plist-get cj/--projectile-revert-state :map)
+                   'projectile-compile-cmd-map))
+    (should (equal (plist-get cj/--projectile-revert-state :root) "/p/"))
+    (should (equal (plist-get cj/--projectile-revert-state :prior) "make build"))))
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-no-prior-stores-nil ()
+  "Normal: when no cmd is cached, captures :prior nil — distinct from
+\"didn't capture at all\" because :map and :root are still set."
+  (let* ((cj/--projectile-revert-state nil)
+         (projectile-test-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      (cj/--projectile-capture-cmd 'projectile-test-cmd-map))
+    (should (eq (plist-get cj/--projectile-revert-state :map)
+                'projectile-test-cmd-map))
+    (should (null (plist-get cj/--projectile-revert-state :prior)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-nil-root-leaves-state-nil ()
+  "Boundary: when no project root resolves, state stays nil so the
+finish hook treats it as a no-op."
+  (let ((cj/--projectile-revert-state nil)
+        (projectile-compile-cmd-map (make-hash-table :test 'equal)))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () nil)))
+      (cj/--projectile-capture-cmd 'projectile-compile-cmd-map))
+    (should (null cj/--projectile-revert-state))))
+
+;;; Error Cases
+
+(ert-deftest test-dev-fkeys-projectile-capture-cmd-unbound-map-leaves-state-nil ()
+  "Error: when the cmd-map symbol is unbound (projectile not loaded),
+state stays nil and no error is raised."
+  (let ((cj/--projectile-revert-state nil))
+    (cl-letf (((symbol-function 'cj/--f4-project-root) (lambda () "/p/")))
+      ;; Use a clearly-unbound symbol to simulate projectile-not-loaded.
+      (cj/--projectile-capture-cmd 'cj-test--definitely-not-bound-xyzzy))
+    (should (null cj/--projectile-revert-state))))
+
+(provide 'test-dev-fkeys--projectile-capture-cmd)
+;;; test-dev-fkeys--projectile-capture-cmd.el ends here