fix(story-mode): a helper reporting back is heard in its own words

From review round 9: a background job's page showed only Claude Code's
line 'Agent "Helper B: write extra pytest tests" finished', so what the
helper said about its own work vanished, here that it had never run its
tests against the real wordcount.py.

The notice balloon now carries the helper's report like Claude's last
words (its first sentence and the key sentences from the rest):
'"Helper B: write extra pytest tests" reports: I wrote the file:
tests/test_extra.py It has 18 test cases … I haven't run it against the
real wordcount.py.' A report that is only a path is its file name, and
absolute paths keep their last two parts, so a long path does not push
the sentence that matters out of a phone's balloon.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/fixtures/story-corpus/background-helpers-reports.expected.json

@@ -96,7 +96,7 @@
         "ok": null,
         "story": "A background job reports back.",
         "director": "Prompt · 6 words · task",
-        "balloon": "Agent \"Helper A: write README.md\" finished",
+        "balloon": "\"Helper A: write README.md\" reports: README.md",
         "tests": null,
         "roundsOk": null,
         "printed": null,
@@ -147,7 +147,7 @@
         "ok": null,
         "story": "A background job reports back.",
         "director": "Prompt · 8 words · task",
-        "balloon": "Agent \"Helper B: write extra pytest tests\" finished",
+        "balloon": "\"Helper B: write extra pytest tests\" reports: I wrote the file: tests/test_extra.py It has 18 test cases and I worked out each expected value by hand. I haven't run it against the real wordcount.py.",
         "tests": null,
         "roundsOk": null,
         "printed": null,
@@ -328,7 +328,7 @@
         "ok": null,
         "story": "A background job reports back.",
         "director": "Prompt · 6 words · task",
-        "balloon": "Agent \"Helper: write CHANGELOG.md slowly\" finished",
+        "balloon": "\"Helper: write CHANGELOG.md slowly\" reports: CHANGELOG.md",
         "tests": null,
         "roundsOk": null,
         "printed": null,

test/fixtures/story-corpus/bash-script-background-helper.expected.json

@@ -119,7 +119,7 @@
         "ok": null,
         "story": "A background job reports back.",
         "director": "Prompt · 7 words · task",
-        "balloon": "Agent \"Write README for rename script\" finished",
+        "balloon": "\"Write README for rename script\" reports: I wrote the README at story-review-c/README.md. It covers the description, requirements, usage with dry-run, real-run and re-run sample output, name clashes, notes and limitations, and exit codes. The script wasn't there when I started, but it appeared while I was writing, so I read it (without running or editing it) and matched the README to it: it agrees with the spec, and I added the exact summary line (Done: N renamed, M skipped.), the -- option for a directory name starting with -, the…",
         "tests": null,
         "roundsOk": null,
         "printed": null,

test/fixtures/story-corpus/text-plan-dry-run-helper.expected.json

@@ -133,7 +133,7 @@
         "ok": null,
         "story": "A background job reports back.",
         "director": "Prompt · 6 words · task",
-        "balloon": "Agent \"Write README for csvstat\" finished",
+        "balloon": "\"Write README for csvstat\" reports: I wrote README.md and committed it on its own on feat/csvstat. The README has every section you asked for and no badges.",
         "tests": null,
         "roundsOk": null,
         "printed": null,

test/story-corpus.test.ts

@@ -193,6 +193,16 @@ describe('Story Mode on real sessions', () => {
     expect(panel).toBeTruthy();
   });
 
+  it('a helper reporting back is heard in its own words, not only "finished" (round 9)', () => {
+    const [, readme, extra] = pagesOf('background-helpers-reports');
+    expect(readme.panels[0].balloon).toBe('"Helper A: write README.md" reports: README.md');
+    // What the helper did not do is on the page, and a long path does not crowd it out.
+    expect(extra.panels[0].balloon).toMatch(
+      /^"Helper B: write extra pytest tests" reports: I wrote the file: tests\/test_extra\.py /
+    );
+    expect(extra.panels[0].balloon).toMatch(/I haven't run it against the real wordcount\.py\.$/);
+  });
+
   it('a blocked command ends a turn where nothing worked, without a celebration', () => {
     const last = pagesOf('teammates-then-interrupt')[4];
     expect(last.panels.map((p) => p.story)).toEqual([