feat(lanes): name the files behind a lane's uncommitted counts

GET /api/lanes/:id/git now returns `files`, the raw `git status --porcelain`
lines the dirty/untracked counts were already parsed from, capped at 20 so a
lane mid-`npm install` cannot ship thousands of paths through a polled
endpoint. The lane card hovers them as the tooltip on its
"N modified · N untracked" text, appending "… +N" when the cap bit.

No new subprocess and no new endpoint — statusCounts was counting those lines
and throwing them away.

server/__tests__/worktree.test.js

@@ -100,6 +100,8 @@ describe("worktree", () => {
     assert.equal(s.dirty, 1);
     assert.equal(s.untracked, 1); // node_modules is ignored, so it does not count
     assert.match(s.head, /^[0-9a-f]{7,40}$/);
+    // The same lines the counts came from, so a caller can name the files.
+    assert.deepEqual(s.files.sort(), [" M README.md", "?? scratch.txt"]);
     // The fixture has no remotes. Given the lane's base branch, unpushedCount
     // measures base..HEAD — this worktree has committed nothing of its own, so 0.
     assert.equal(await wt.unpushedCount(dir, "main"), 0);

server/lib/worktree.js

@@ -16,6 +16,8 @@ const execFileAsync = promisify(execFile);
 
 const LANES_ROOT = process.env.LANES_ROOT || path.join(os.homedir(), ".claude", "agenthub-lanes");
 const PROTECTED_BRANCHES = new Set(["main", "master"]);
+/** Most status lines `statusCounts` reports by name; the counts stay exact. */
+const STATUS_FILE_CAP = 20;
 
 /**
  * Promisified git wrapper. On failure, throws an Error with err.git = { args, code, stderr }.
@@ -549,11 +551,16 @@ async function removeWorktree(lane) {
 /**
  * Parse git status --porcelain to count dirty, untracked, and get HEAD commit.
  * Lines starting with ?? are untracked; others are dirty.
+ *
+ * `files` carries the same lines back verbatim so a caller can show WHICH
+ * files the counts mean, capped because this rides a polled endpoint and a
+ * lane mid-`npm install` can report thousands.
  */
 async function statusCounts(dir) {
   const result = await git(dir, ["status", "--porcelain=v1", "--untracked-files=normal"]);
   let dirty = 0;
   let untracked = 0;
+  const files = [];
 
   for (const line of result.stdout.split("\n")) {
     if (!line.trim()) continue;
@@ -562,13 +569,14 @@ async function statusCounts(dir) {
     } else {
       dirty++;
     }
+    if (files.length < STATUS_FILE_CAP) files.push(line.trimEnd());
   }
 
   // Get short commit hash
   const headResult = await git(dir, ["rev-parse", "--short", "HEAD"]);
   const head = headResult.stdout.trim();
 
-  return { dirty, untracked, head };
+  return { dirty, untracked, head, files };
 }
 
 /**
@@ -581,10 +589,10 @@ async function statusCounts(dir) {
  * caller shows what git says rather than inventing a nicer word for it.
  */
 async function gitFacts(dir) {
-  const { dirty, untracked, head } = await statusCounts(dir);
+  const { dirty, untracked, head, files } = await statusCounts(dir);
   const branch = (await git(dir, ["rev-parse", "--abbrev-ref", "HEAD"])).stdout.trim();
   const subject = (await git(dir, ["log", "-1", "--format=%s"])).stdout.trim();
-  return { branch, head, subject, dirty, untracked };
+  return { branch, head, subject, dirty, untracked, files };
 }
 
 /**

server/openapi-extra/lanes.js

@@ -274,7 +274,7 @@ const paths = {
       responses: {
         200: {
           description:
-            "available:true with {branch, head, subject, dirty, untracked}, or available:false alone.",
+            "available:true with {branch, head, subject, dirty, untracked, files}, or available:false alone. files holds the raw `git status --porcelain` lines behind those counts, capped at 20; the counts themselves are never capped.",
         },
         404: { description: "Lane not found." },
       },