diff --git a/src/main/services/team/TeamTranscriptProjectResolver.ts b/src/main/services/team/TeamTranscriptProjectResolver.ts
index 15afbdc2..f0f2451b 100644
--- a/src/main/services/team/TeamTranscriptProjectResolver.ts
+++ b/src/main/services/team/TeamTranscriptProjectResolver.ts
@@ -241,6 +241,12 @@ interface TeamAffinityFileCacheEntry {
   mtimeMs: number;
   size: number;
   belongsToTeam: boolean;
+  // True when the verdict was decided after inspecting a FULL head window
+  // (>= TEAM_AFFINITY_SCAN_LINES non-empty lines). For append-only transcripts the
+  // head is immutable, so a `false` verdict from a full window stays valid while the
+  // file only grows — letting us cache negatives durably instead of re-streaming
+  // every non-matching transcript on each bootstrap poll.
+  headWindowFull: boolean;
 }
 
 export class TeamTranscriptProjectResolver {
@@ -1031,6 +1037,16 @@ export class TeamTranscriptProjectResolver {
       if (cached.belongsToTeam && fileStat.size >= cached.size) {
         return true;
       }
+      // A `false` decided from a FULL head window is durable while the file only
+      // grows: the first TEAM_AFFINITY_SCAN_LINES lines of an append-only transcript
+      // are immutable, so growth cannot introduce a team mention inside the inspected
+      // window. A shrink/rewrite makes size < cached.size and falls through to a
+      // re-scan below, identically to the positive path. This is the main launch win:
+      // non-matching transcripts in the project dir are no longer re-streamed +
+      // re-parsed on every bootstrap poll.
+      if (!cached.belongsToTeam && cached.headWindowFull && fileStat.size >= cached.size) {
+        return false;
+      }
       if (cached.mtimeMs === fileStat.mtimeMs && cached.size === fileStat.size) {
         return cached.belongsToTeam;
       }
@@ -1039,9 +1055,9 @@ export class TeamTranscriptProjectResolver {
     const stream = createReadStream(filePath, { encoding: 'utf8' });
     const rl = readline.createInterface({ input: stream, crlfDelay: Infinity });
     let belongsToTeam = false;
+    let inspected = 0;
 
     try {
-      let inspected = 0;
       for await (const line of rl) {
         const trimmed = line.trim();
         if (!trimmed) {
@@ -1085,6 +1101,7 @@ export class TeamTranscriptProjectResolver {
       mtimeMs: fileStat.mtimeMs,
       size: fileStat.size,
       belongsToTeam,
+      headWindowFull: inspected >= TEAM_AFFINITY_SCAN_LINES,
     });
     return belongsToTeam;
   }
diff --git a/test/main/services/team/TeamTranscriptProjectResolver.test.ts b/test/main/services/team/TeamTranscriptProjectResolver.test.ts
index 786c048e..696c7911 100644
--- a/test/main/services/team/TeamTranscriptProjectResolver.test.ts
+++ b/test/main/services/team/TeamTranscriptProjectResolver.test.ts
@@ -623,4 +623,97 @@ describe('TeamTranscriptProjectResolver', () => {
     expect(fastContext?.sessionIds).not.toContain('old-member-session');
     expect(fullContext?.sessionIds).toContain('old-member-session');
   });
+
+  // Regression for the launch hot path: non-matching transcripts must not be
+  // re-streamed + re-parsed on every bootstrap poll. A negative verdict decided from
+  // a FULL head window (>= 40 inspected lines) is durable while the file only grows,
+  // because an append-only transcript's head is immutable. Observed via the private
+  // affinity cache: the durable branch returns WITHOUT re-caching, so the cached size
+  // stays at the first scan's size (a re-scan would update it to the grown size).
+  type AffinityCacheEntry = {
+    mtimeMs: number;
+    size: number;
+    belongsToTeam: boolean;
+    headWindowFull: boolean;
+  };
+  type ResolverProbe = {
+    fileBelongsToTeam: (filePath: string, teamName: string) => Promise<boolean>;
+    buildTeamAffinityFileCacheKey: (filePath: string, normalizedTeam: string) => string;
+    teamAffinityFileCache: Map<string, AffinityCacheEntry>;
+  };
+
+  it('caches a full-head-window negative and stops re-scanning a growing non-matching transcript', async () => {
+    await setupClaudeRoot();
+    const resolver = new TeamTranscriptProjectResolver() as unknown as ResolverProbe;
+    const team = 'absent-team';
+    const projectDir = path.join(tmpDir!, 'projects', encodePath('/repo/neg-durable'));
+    await fs.mkdir(projectDir, { recursive: true });
+    const jsonlPath = path.join(projectDir, 'unrelated.jsonl');
+    const mkLine = (i: number) =>
+      JSON.stringify({ type: 'user', message: { role: 'user', content: `unrelated line ${i}` } });
+    // 45 non-empty lines, none mentioning the team -> full head window (40) inspected.
+    await fs.writeFile(
+      jsonlPath,
+      `${Array.from({ length: 45 }, (_, i) => mkLine(i)).join('\n')}\n`,
+      'utf8'
+    );
+
+    expect(await resolver.fileBelongsToTeam(jsonlPath, team)).toBe(false);
+    const key = resolver.buildTeamAffinityFileCacheKey(jsonlPath, team.toLowerCase());
+    const first = resolver.teamAffinityFileCache.get(key);
+    expect(first?.belongsToTeam).toBe(false);
+    expect(first?.headWindowFull).toBe(true);
+    const sizeAfterFirst = first!.size;
+
+    // Append-only growth: size grows, mtime changes, but the inspected head is fixed.
+    await fs.appendFile(jsonlPath, `${mkLine(100)}\n`);
+    expect(await resolver.fileBelongsToTeam(jsonlPath, team)).toBe(false);
+    // Durable negative: the cache entry was NOT re-written (no re-scan), so its size
+    // is still the original, smaller size.
+    expect(resolver.teamAffinityFileCache.get(key)?.size).toBe(sizeAfterFirst);
+  });
+
+  // Correctness guard: a SHORT-file negative (head window not yet full) is NOT durable
+  // and must be re-scanned on growth, so a team mention that lands inside the first 40
+  // lines is still detected (the verdict flips to true).
+  it('re-scans a short-file negative on growth and flips to true when the head gains a team mention', async () => {
+    await setupClaudeRoot();
+    const resolver = new TeamTranscriptProjectResolver() as unknown as ResolverProbe;
+    const team = 'team-x';
+    const projectDir = path.join(tmpDir!, 'projects', encodePath('/repo/short-neg'));
+    await fs.mkdir(projectDir, { recursive: true });
+    const jsonlPath = path.join(projectDir, 'short.jsonl');
+    // Only 3 lines, none mentioning the team -> partial head window (not durable).
+    await fs.writeFile(
+      jsonlPath,
+      `${[0, 1, 2]
+        .map((i) => JSON.stringify({ type: 'user', message: { role: 'user', content: `hi ${i}` } }))
+        .join('\n')}\n`,
+      'utf8'
+    );
+
+    expect(await resolver.fileBelongsToTeam(jsonlPath, team)).toBe(false);
+    const key = resolver.buildTeamAffinityFileCacheKey(jsonlPath, team.toLowerCase());
+    const first = resolver.teamAffinityFileCache.get(key);
+    expect(first?.headWindowFull).toBe(false);
+    const sizeAfterFirst = first!.size;
+
+    // Append a line whose text content mentions the team (still within the first 40 lines).
+    await fs.appendFile(
+      jsonlPath,
+      `${JSON.stringify({
+        type: 'user',
+        message: {
+          role: 'user',
+          content: [
+            { type: 'text', text: `Current durable team context:\n- Team name: ${team}` },
+          ],
+        },
+      })}\n`
+    );
+    expect(await resolver.fileBelongsToTeam(jsonlPath, team)).toBe(true); // re-scanned -> flips
+    const second = resolver.teamAffinityFileCache.get(key);
+    expect(second?.belongsToTeam).toBe(true);
+    expect(second!.size).toBeGreaterThan(sizeAfterFirst); // re-scanned + re-cached
+  });
 });