feat: write transcript for CLI provider runs [AI-assisted]

CLI backends (claude-cli, codex-cli, etc.) don't normally save session
transcripts because they run as external processes. This causes issues
with subagent announce flow - when a CLI-backed subagent completes, the
main agent can't read the reply because no transcript exists.

This change writes a JSONL transcript file after CLI provider runs
complete, using the same format as embedded Pi sessions:
- Session header with version, id, timestamp, cwd
- Message entry with assistant role, content, timestamp, usage

The transcript path is resolved from the session key/id and agent id,
matching the embedded runner's behavior.

Transcript writes are best-effort and won't fail the run.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/auto-reply/reply/agent-runner-execution.ts

@@ -1,5 +1,6 @@
 import crypto from "node:crypto";
 import fs from "node:fs";
+import path from "node:path";
 import { resolveAgentModelFallbacksOverride } from "../../agents/agent-scope.js";
 import { runCliAgent } from "../../agents/cli-runner.js";
 import { getCliSessionId } from "../../agents/cli-session.js";
@@ -192,6 +193,50 @@ export async function runAgentTurnWithFallback(params: {
                     data: { text: cliText },
                   });
                 }
+                // Write CLI result to transcript for subagent announce flow
+                if (cliText && params.sessionKey && params.followupRun.run.sessionId) {
+                  try {
+                    const agentId = resolveAgentIdFromSessionKey(params.sessionKey);
+                    const transcriptPath = resolveSessionTranscriptPath(
+                      params.followupRun.run.sessionId,
+                      agentId,
+                    );
+                    // Ensure directory exists
+                    fs.mkdirSync(path.dirname(transcriptPath), { recursive: true });
+                    // Create session header if file doesn't exist
+                    if (!fs.existsSync(transcriptPath)) {
+                      const header = {
+                        type: "session",
+                        version: 1,
+                        id: params.followupRun.run.sessionId,
+                        timestamp: new Date().toISOString(),
+                        cwd: process.cwd(),
+                      };
+                      fs.writeFileSync(transcriptPath, JSON.stringify(header) + "\n", "utf-8");
+                    }
+                    // Append assistant message
+                    const messageEntry = {
+                      type: "message",
+                      id: crypto.randomUUID().slice(0, 8),
+                      timestamp: new Date().toISOString(),
+                      message: {
+                        role: "assistant",
+                        content: [{ type: "text", text: cliText }],
+                        timestamp: Date.now(),
+                        stopReason: "cli",
+                        usage: result.meta?.agentMeta?.usage ?? {
+                          input: 0,
+                          output: 0,
+                          totalTokens: 0,
+                        },
+                      },
+                    };
+                    fs.appendFileSync(transcriptPath, JSON.stringify(messageEntry) + "\n", "utf-8");
+                  } catch (err) {
+                    // Best effort - don't fail the run if transcript write fails
+                    logVerbose(`CLI transcript write failed: ${String(err)}`);
+                  }
+                }
                 emitAgentEvent({
                   runId,
                   stream: "lifecycle",