feat(man): re-enable man sync test with runtime dependency check

Re-enable the `man` test with a `which` check that panics with a
diagnostic message and `TEST_SKIP` hint when `man` is not installed,
following the same pattern as `fs_errors` and `cross_device_excludes_mount`.

Add `man-db` to CI's external test dependency installation step and
document it in CONTRIBUTING.md alongside the existing FUSE dependencies.

https://claude.ai/code/session_01CrXuWDMVQsiUBoy6ceACsF

Author: claude

.github/workflows/test.yaml

@@ -46,7 +46,7 @@ jobs:
         if: runner.os == 'Linux'
         run: |
           sudo apt update
-          sudo apt install -y squashfs-tools squashfuse fuse3
+          sudo apt install -y squashfs-tools squashfuse fuse3 man-db
 
       - name: Test (dev)
         shell: bash

CONTRIBUTING.md

@@ -358,6 +358,7 @@ Some integration tests require external (non-Cargo) tools that are **not** manag
 - `squashfs-tools` (provides `mksquashfs`) — cross-device (`--one-file-system`) FUSE test
 - `squashfuse` (provides `squashfuse`) — cross-device (`--one-file-system`) FUSE test
 - `fuse3` (provides `fusermount3`, `/dev/fuse`) — cross-device (`--one-file-system`) FUSE test
+- `man-db` (provides `man`) — man page sync test
 
 Tests that need these tools will panic with a diagnostic message if they are missing. The panic message includes the specific `TEST_SKIP` variable to skip the test via `./test.sh`.
 

tests/sync_man_page.rs

@@ -40,7 +40,14 @@ fn roff() {
 }
 
 #[test]
-#[ignore = "requires man(1); run with --include-ignored to check"]
 fn man() {
+    if which::which("man").is_err() {
+        panic!(
+            "{}\n{}",
+            "error: This test requires `man` but it was not found.",
+            "hint: Install `man-db` for your platform, \
+             or rerun via `TEST_SKIP='man' ./test.sh` to skip this test.",
+        );
+    }
     check("man", "1");
 }