perf: share bootstrap transcript tail parse across members

During launch, the bootstrap-wait loop polls each member and, per member, re-read
and re-JSON.parsed the same growing transcript tail (readRecentBootstrapTranscriptOutcome
was the top main-thread JS hotspot at ~21% during bootstrap, ~40% with its helpers).
The same file was parsed once per member per poll.

Memoize the parsed tail by (filePath, mtime, size) in a shared cache so the file is
read + parsed once per change and reused across all members. The per-member filter
and failure/success scan is byte-for-byte the same logic; only the redundant read +
JSON.parse is removed. Cache is bounded (LRU, same cap as the outcome cache) and
invalidated on mtime/size change, matching the existing outcome cache semantics.

Adds a test asserting the tail is parsed once and shared while per-member outcome
detection is unchanged.

src/main/services/team/TeamProvisioningService.ts

@@ -704,6 +704,19 @@ interface BootstrapTranscriptOutcomeCandidate {
   parsedAgentName: string | null;
 }
 
+interface ParsedBootstrapTranscriptTailLine {
+  rawTimestamp: string | null;
+  timestampMs: number;
+  text: string | null;
+  parsedAgentName: string | null;
+}
+
+interface ParsedBootstrapTranscriptTailCacheEntry {
+  mtimeMs: number;
+  size: number;
+  lines: ParsedBootstrapTranscriptTailLine[];
+}
+
 import type {
   ActiveToolCall,
   AgentActionMode,
@@ -3375,6 +3388,13 @@ export class TeamProvisioningService {
     string,
     BootstrapTranscriptOutcomeCacheEntry
   >();
+  // Shared parsed-tail cache keyed by filePath (validated by mtime+size) so the
+  // same growing transcript is read + JSON.parsed ONCE per change instead of once
+  // per member per poll. The per-member outcome scan below is unchanged.
+  private readonly parsedBootstrapTranscriptTailCache = new Map<
+    string,
+    ParsedBootstrapTranscriptTailCacheEntry
+  >();
   private readonly bootstrapTranscriptOutcomeLookupCache = new Map<
     string,
     BootstrapTranscriptOutcomeLookupCacheEntry
@@ -30303,44 +30323,24 @@ export class TeamProvisioningService {
       if (cached && cached.mtimeMs === stat.mtimeMs && cached.size === stat.size) {
         return cached.outcome;
       }
-      const start = Math.max(0, stat.size - TeamProvisioningService.BOOTSTRAP_FAILURE_TAIL_BYTES);
-      const buffer = Buffer.alloc(stat.size - start);
-      if (buffer.length === 0) {
-        return null;
-      }
-      await handle.read(buffer, 0, buffer.length, start);
-      const lines = buffer.toString('utf8').split('\n');
-      if (start > 0) {
-        lines.shift();
-      }
+      // Parse the transcript tail once per (filePath, mtime, size) and share it
+      // across members. The per-member filter/scan below is byte-for-byte the same
+      // logic as before; only the redundant read + JSON.parse is now memoized.
+      const parsedLines = await this.getParsedBootstrapTranscriptTail(handle, filePath, stat);
       const shouldCollectBootstrapContext = options.allowAnonymousFailure !== true;
       const bootstrapContextMembers = new Set<string>();
       const candidates: BootstrapTranscriptOutcomeCandidate[] = [];
-      for (const rawLine of lines) {
-        const line = rawLine?.trim();
-        if (!line) continue;
-        let parsed: { timestamp?: unknown } | null = null;
-        try {
-          parsed = JSON.parse(line) as { timestamp?: unknown };
-        } catch {
-          continue;
-        }
-        const timestampMs =
-          typeof parsed.timestamp === 'string' ? Date.parse(parsed.timestamp) : Number.NaN;
+      for (const parsedLine of parsedLines) {
+        const { timestampMs, parsedAgentName, text, rawTimestamp } = parsedLine;
         if (sinceMs != null && (!Number.isFinite(timestampMs) || timestampMs < sinceMs)) {
           continue;
         }
-        const parsedAgentName =
-          typeof (parsed as { agentName?: unknown }).agentName === 'string'
-            ? (parsed as { agentName?: string }).agentName?.trim().toLowerCase() || null
-            : null;
         if (
           parsedAgentName &&
           !matchesObservedMemberNameForExpected(parsedAgentName, normalizedMemberName)
         ) {
           continue;
         }
-        const text = extractTranscriptMessageText(parsed);
         if (!text) {
           continue;
         }
@@ -30354,9 +30354,7 @@ export class TeamProvisioningService {
         candidates.push({
           text,
           observedAt:
-            typeof parsed.timestamp === 'string' && parsed.timestamp.trim().length > 0
-              ? parsed.timestamp.trim()
-              : new Date().toISOString(),
+            rawTimestamp && rawTimestamp.length > 0 ? rawTimestamp : new Date().toISOString(),
           parsedAgentName,
         });
       }
@@ -30428,6 +30426,73 @@ export class TeamProvisioningService {
     ].join('\0');
   }
 
+  private async getParsedBootstrapTranscriptTail(
+    handle: fs.promises.FileHandle,
+    filePath: string,
+    stat: { mtimeMs: number; size: number }
+  ): Promise<ParsedBootstrapTranscriptTailLine[]> {
+    const cached = this.parsedBootstrapTranscriptTailCache.get(filePath);
+    if (cached && cached.mtimeMs === stat.mtimeMs && cached.size === stat.size) {
+      return cached.lines;
+    }
+    const lines: ParsedBootstrapTranscriptTailLine[] = [];
+    const start = Math.max(0, stat.size - TeamProvisioningService.BOOTSTRAP_FAILURE_TAIL_BYTES);
+    const length = stat.size - start;
+    if (length > 0) {
+      const buffer = Buffer.alloc(length);
+      await handle.read(buffer, 0, length, start);
+      const rawLines = buffer.toString('utf8').split('\n');
+      if (start > 0) {
+        rawLines.shift();
+      }
+      for (const rawLine of rawLines) {
+        const line = rawLine?.trim();
+        if (!line) continue;
+        let parsed: { timestamp?: unknown; agentName?: unknown } | null = null;
+        try {
+          parsed = JSON.parse(line) as { timestamp?: unknown; agentName?: unknown };
+        } catch {
+          continue;
+        }
+        const rawTimestamp =
+          typeof parsed.timestamp === 'string' && parsed.timestamp.trim().length > 0
+            ? parsed.timestamp.trim()
+            : null;
+        const timestampMs =
+          typeof parsed.timestamp === 'string' ? Date.parse(parsed.timestamp) : Number.NaN;
+        const parsedAgentName =
+          typeof parsed.agentName === 'string'
+            ? parsed.agentName.trim().toLowerCase() || null
+            : null;
+        const text = extractTranscriptMessageText(parsed);
+        lines.push({ rawTimestamp, timestampMs, text, parsedAgentName });
+      }
+    }
+    this.setParsedBootstrapTranscriptTailCacheEntry(filePath, {
+      mtimeMs: stat.mtimeMs,
+      size: stat.size,
+      lines,
+    });
+    return lines;
+  }
+
+  private setParsedBootstrapTranscriptTailCacheEntry(
+    filePath: string,
+    entry: ParsedBootstrapTranscriptTailCacheEntry
+  ): void {
+    if (
+      !this.parsedBootstrapTranscriptTailCache.has(filePath) &&
+      this.parsedBootstrapTranscriptTailCache.size >=
+        TeamProvisioningService.BOOTSTRAP_TRANSCRIPT_OUTCOME_CACHE_MAX_ENTRIES
+    ) {
+      const oldestKey = this.parsedBootstrapTranscriptTailCache.keys().next().value;
+      if (oldestKey) {
+        this.parsedBootstrapTranscriptTailCache.delete(oldestKey);
+      }
+    }
+    this.parsedBootstrapTranscriptTailCache.set(filePath, entry);
+  }
+
   private setBootstrapTranscriptOutcomeCacheEntry(
     cacheKey: string,
     entry: BootstrapTranscriptOutcomeCacheEntry

test/main/services/team/TeamProvisioningService.test.ts

@@ -21167,6 +21167,47 @@ describe('TeamProvisioningService', () => {
     });
   });
 
+  it('parses a bootstrap transcript tail once and shares it across members', async () => {
+    const teamName = 'zz-unit-bootstrap-transcript-shared-parse';
+    const transcriptPath = path.join(tempProjectsBase, 'bootstrap-shared-parse.jsonl');
+    await fsPromises.writeFile(
+      transcriptPath,
+      `${JSON.stringify({
+        timestamp: '2026-05-24T09:25:42.904Z',
+        agentName: 'alice',
+        text: `member briefing for alice on team "${teamName}" (${teamName}). Ready.`,
+      })}\n`,
+      'utf8'
+    );
+    const updatedAt = new Date(Date.now() + 5_000);
+    await fsPromises.utimes(transcriptPath, updatedAt, updatedAt);
+
+    const svc = new TeamProvisioningService();
+
+    const aliceOutcome = await privateHarness(svc).readRecentBootstrapTranscriptOutcome(
+      transcriptPath,
+      null,
+      'alice',
+      teamName
+    );
+    const bobOutcome = await privateHarness(svc).readRecentBootstrapTranscriptOutcome(
+      transcriptPath,
+      null,
+      'bob',
+      teamName
+    );
+
+    // Per-member detection is unchanged: alice's briefing is a success, the same
+    // line is not attributed to bob.
+    expect(aliceOutcome).toMatchObject({ kind: 'success', source: 'member_briefing' });
+    expect(bobOutcome).toBeNull();
+    // The transcript tail is parsed once and shared: a single cache entry for the
+    // file rather than one parse per member.
+    expect((svc as unknown as Record<string, Map<string, unknown>>).parsedBootstrapTranscriptTailCache.size).toBe(
+      1
+    );
+  });
+
   it('caches persisted bootstrap transcript outcome lookup between close polling reads', async () => {
     vi.useFakeTimers();
     vi.setSystemTime(new Date('2026-05-03T12:00:00.000Z'));