fix(#648): anchor antigravity's working line to the start of a row

_probePaneWorking() tests the pattern against the whole pane, so an answer
that quoted the spinner row (an agent explaining this entry: it matches
`⣯  Generating...`) kept the session busy for as long as the text was on
screen. Anchored like gemini's braille branch; every agy capture draws the
spinner at column 0. The prose test now covers the quoted row.

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

src/config/cli-registry/stock.ts

@@ -1012,9 +1012,13 @@ const ANTIGRAVITY: CliEntry = {
     // too. The footer hint is drawn only at rest, and the turn's last repaint carries it.
     // The schema caps a glyph at 8 characters, so this is the head of `? for shortcuts`. It also
     // keeps the submit verifier inert (no row starts with it and holds prompt text).
+    // The working line is anchored to the start of a row, like gemini's braille branch: the
+    // idle probe tests it against the whole pane, and an answer that QUOTES the spinner row
+    // (an agent explaining this entry) would otherwise hold the tab busy while it is on screen.
+    // Every `agy` capture draws the spinner at column 0.
     workDetect: {
       promptGlyph: '? for sh',
-      workingLine: String.raw`[⠀-⣿]  [A-Z][A-Za-z ]{2,30}(?:\.\.\.|…)`,
+      workingLine: String.raw`(?:^|\n)[⠀-⣿]  [A-Z][A-Za-z ]{2,30}(?:\.\.\.|…)`,
     },
     // Like codex: an ABSENT config already defaults safe (no bypass flag), so only a
     // SENT config needs the flag forced off — nothing is materialized.

test/session-activity.test.ts

@@ -1018,6 +1018,8 @@ describe("antigravity's work-detection descriptor", () => {
     expect(working().test(AGY_AT_REST)).toBe(false);
     expect(working().test(AGY_CONFIRM)).toBe(false);
     expect(working().test('Loading... is what the spinner label reads\n')).toBe(false);
+    // An answer that quotes the spinner row mid-line must not hold the tab busy.
+    expect(working().test(`  ok\n  it matches \`⣯  Generating...\` in the pane\n${AGY_RULE}\n>\n`)).toBe(false);
   });
 
   it('names the footer hint the turn end carries, and no working repaint does', () => {