CB-634: write the overlay exclude to the common git dir, not the per-worktree gitdir

git reads info/exclude from the common dir for a linked worktree (only
info/sparse-checkout is per-worktree), so the entry written into
<common>/worktrees/<name>/info/exclude was never honoured and CLAUDE.local.md
showed as untracked -- at risk of being swept into a worker's PR. Derive the
common dir (<common>/worktrees/<name> -> <common>) and write there. Found by
dogfooding a real spawn on fleet01; the test now uses the real worktree layout
and asserts the entry lands in the common dir, not the per-worktree gitdir.

bridged/src/main/java/dev/ltms/fleet/member/ClaudeCodeLauncher.java

@@ -356,7 +356,8 @@ public final class ClaudeCodeLauncher extends HerdrPeerLauncher {
     /**
      * Deliver the shared IDE guidance ({@link PeerLauncher#ideOverlayText}) as an on-disk
      * {@code CLAUDE.local.md} overlay beside the project's own {@code CLAUDE.md} (CB-634), and
-     * register the overlay in the worktree's {@code info/exclude} so it never shows as untracked.
+     * register the overlay in the repository's common {@code info/exclude} so it never shows as
+     * untracked (git reads a worktree's excludes from the common dir, not the per-worktree gitdir).
      *
      * <p><strong>Safety gate:</strong> the overlay is written ONLY when {@code cwd/.git} is a
      * <em>regular file</em> — a provisioned worktree keeps a {@code .git} FILE holding a
@@ -382,7 +383,16 @@ public final class ClaudeCodeLauncher extends HerdrPeerLauncher {
             if (!gitDir.isAbsolute()) {
                 gitDir = Path.of(cwd).resolve(gitDir).normalize();
             }
-            Path exclude = gitDir.resolve("info").resolve("exclude");
+            // git reads info/exclude from the COMMON dir, never the per-worktree gitdir (only
+            // info/sparse-checkout is per-worktree). A provisioned worktree's gitdir is
+            // <common>/worktrees/<name>, so the common dir is two levels up; writing the entry into
+            // the per-worktree gitdir leaves it un-honoured and the overlay shows as untracked.
+            Path commonDir = gitDir;
+            if (gitDir.getParent() != null && gitDir.getParent().getFileName() != null
+                    && "worktrees".equals(gitDir.getParent().getFileName().toString())) {
+                commonDir = gitDir.getParent().getParent();
+            }
+            Path exclude = commonDir.resolve("info").resolve("exclude");
             Files.createDirectories(exclude.getParent());
             String overlayLine = "CLAUDE.local.md";
             if (!Files.exists(exclude) || Files.readAllLines(exclude).stream().noneMatch(overlayLine::equals)) {

bridged/src/test/java/dev/ltms/fleet/member/ClaudeCodeLauncherTest.java

@@ -138,14 +138,17 @@ class ClaudeCodeLauncherTest {
     }
 
     // CB-634: the IDE guidance is delivered as a CLAUDE.local.md overlay (written only into a
-    // provisioned worktree — cwd with a `.git` FILE) and registered in the worktree's info/exclude.
+    // provisioned worktree — cwd with a `.git` FILE) and registered in the repository's COMMON
+    // info/exclude. git reads a worktree's excludes from the common dir, not the per-worktree
+    // gitdir (only info/sparse-checkout is per-worktree), so a real provisioned layout
+    // <common>/worktrees/<name> must land the entry in <common>/info/exclude.
 
     @Test
-    void writeIdeOverlayWritesClaudeLocalAndAddsItToInfoExclude(@TempDir Path root) throws Exception {
+    void writeIdeOverlayWritesClaudeLocalAndAddsItToCommonInfoExclude(@TempDir Path root) throws Exception {
         Path worktree = Files.createDirectory(root.resolve("worktree"));
-        Path gitDir = Files.createDirectory(root.resolve("gitdir"));
-        Files.createDirectories(gitDir.resolve("info"));
-        // A provisioned worktree keeps its gitdir as a `.git` FILE holding a gitdir: <path> pointer.
+        // Real worktree layout: the .git FILE points at <common>/worktrees/<name>.
+        Path commonDir = Files.createDirectory(root.resolve("dotgit"));
+        Path gitDir = Files.createDirectories(commonDir.resolve("worktrees").resolve("wt1"));
         Files.writeString(worktree.resolve(".git"), "gitdir: " + gitDir);
 
         FakeHerdr herdr = new FakeHerdr();
@@ -156,10 +159,12 @@ class ClaudeCodeLauncherTest {
         assertTrue(Files.exists(overlay), "the overlay is written beside the project's CLAUDE.md");
         assertTrue(Files.readString(overlay).contains("project_path: \"" + worktree + "\""),
                 "the overlay pins every ide_* call to the member's own worktree");
-        Path exclude = gitDir.resolve("info").resolve("exclude");
-        assertTrue(Files.exists(exclude), "info/exclude is created from the gitdir pointer");
-        assertTrue(Files.readAllLines(exclude).contains("CLAUDE.local.md"),
-                "the overlay is registered so it never shows as untracked");
+        Path commonExclude = commonDir.resolve("info").resolve("exclude");
+        assertTrue(Files.exists(commonExclude), "info/exclude is created in the COMMON git dir");
+        assertTrue(Files.readAllLines(commonExclude).contains("CLAUDE.local.md"),
+                "the overlay is registered in the common exclude git actually honours for a worktree");
+        assertFalse(Files.exists(gitDir.resolve("info").resolve("exclude")),
+                "the entry must NOT go to the per-worktree gitdir, which git ignores for excludes");
     }
 
     @Test