diff --git a/container/agent-runner/src/poll-loop.ts b/container/agent-runner/src/poll-loop.ts
index e688eab5f..ca081f065 100644
--- a/container/agent-runner/src/poll-loop.ts
+++ b/container/agent-runner/src/poll-loop.ts
@@ -58,6 +58,19 @@ export async function runPollLoop(config: PollLoopConfig): Promise<void> {
   // a Codex thread id never gets handed to Claude or vice versa.
   let continuation: string | undefined = migrateLegacyContinuation(config.providerName);
 
+  // Before resuming, drop a session whose on-disk transcript has grown too
+  // large/old to cold-resume within the host's idle ceiling. Without this a
+  // long-lived hub keeps trying to reload an ever-growing .jsonl, hangs the
+  // first turn, and gets killed before it can reply (then repeats forever).
+  if (continuation) {
+    const rotateReason = config.provider.maybeRotateContinuation?.(continuation, config.cwd);
+    if (rotateReason) {
+      log(`Rotating session — ${rotateReason}; starting fresh`);
+      clearContinuation(config.providerName);
+      continuation = undefined;
+    }
+  }
+
   if (continuation) {
     log(`Resuming agent session ${continuation}`);
   }
diff --git a/container/agent-runner/src/providers/claude.rotate.test.ts b/container/agent-runner/src/providers/claude.rotate.test.ts
new file mode 100644
index 000000000..2d22f243e
--- /dev/null
+++ b/container/agent-runner/src/providers/claude.rotate.test.ts
@@ -0,0 +1,89 @@
+import { describe, it, expect, beforeEach, afterEach } from 'bun:test';
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+
+import { ClaudeProvider } from './claude.js';
+
+// maybeRotateContinuation guards the cold-resume failure mode: a long-lived
+// session whose on-disk transcript has grown so large (or old) that the SDK
+// can't reload it before the host's idle ceiling kills the container.
+
+let tmp: string;
+let prevHome: string | undefined;
+let prevConv: string | undefined;
+let prevBytes: string | undefined;
+let prevDays: string | undefined;
+
+const PROJECT_DIR = '-workspace-agent';
+const CWD = '/workspace/agent';
+
+function writeTranscript(sessionId: string, bytes: number, firstTs?: string): string {
+  const dir = path.join(tmp, '.claude', 'projects', PROJECT_DIR);
+  fs.mkdirSync(dir, { recursive: true });
+  const p = path.join(dir, `${sessionId}.jsonl`);
+  const first =
+    JSON.stringify({
+      type: 'user',
+      timestamp: firstTs ?? new Date().toISOString(),
+      message: { role: 'user', content: 'hello' },
+    }) + '\n';
+  const filler = 'x'.repeat(Math.max(0, bytes - first.length));
+  fs.writeFileSync(p, first + filler);
+  return p;
+}
+
+beforeEach(() => {
+  tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'claude-rotate-'));
+  prevHome = process.env.HOME;
+  prevConv = process.env.NANOCLAW_CONVERSATIONS_DIR;
+  prevBytes = process.env.CLAUDE_TRANSCRIPT_ROTATE_BYTES;
+  prevDays = process.env.CLAUDE_TRANSCRIPT_ROTATE_AGE_DAYS;
+  process.env.HOME = tmp;
+  delete process.env.CLAUDE_CONFIG_DIR;
+  process.env.NANOCLAW_CONVERSATIONS_DIR = path.join(tmp, 'conversations');
+});
+
+afterEach(() => {
+  const restore = (k: string, v: string | undefined) => (v === undefined ? delete process.env[k] : (process.env[k] = v));
+  restore('HOME', prevHome);
+  restore('NANOCLAW_CONVERSATIONS_DIR', prevConv);
+  restore('CLAUDE_TRANSCRIPT_ROTATE_BYTES', prevBytes);
+  restore('CLAUDE_TRANSCRIPT_ROTATE_AGE_DAYS', prevDays);
+  fs.rmSync(tmp, { recursive: true, force: true });
+});
+
+describe('ClaudeProvider.maybeRotateContinuation', () => {
+  it('keeps a small, recent transcript (returns null, leaves file in place)', () => {
+    process.env.CLAUDE_TRANSCRIPT_ROTATE_BYTES = String(1024 * 1024);
+    const p = writeTranscript('sess-small', 4096);
+    const provider = new ClaudeProvider();
+    expect(provider.maybeRotateContinuation('sess-small', CWD)).toBeNull();
+    expect(fs.existsSync(p)).toBe(true);
+  });
+
+  it('rotates an oversized transcript (returns reason, moves the .jsonl aside)', () => {
+    process.env.CLAUDE_TRANSCRIPT_ROTATE_BYTES = String(64 * 1024);
+    const p = writeTranscript('sess-big', 200 * 1024);
+    const provider = new ClaudeProvider();
+    const reason = provider.maybeRotateContinuation('sess-big', CWD);
+    expect(reason).toContain('MB');
+    expect(fs.existsSync(p)).toBe(false); // original moved out of the resume path
+    const dir = path.dirname(p);
+    expect(fs.readdirSync(dir).some((f) => f.startsWith('sess-big.jsonl.rotated-'))).toBe(true);
+  });
+
+  it('rotates an aged transcript even when small', () => {
+    process.env.CLAUDE_TRANSCRIPT_ROTATE_BYTES = String(1024 * 1024);
+    process.env.CLAUDE_TRANSCRIPT_ROTATE_AGE_DAYS = '7';
+    const old = new Date(Date.now() - 10 * 86400_000).toISOString();
+    writeTranscript('sess-old', 2048, old);
+    const provider = new ClaudeProvider();
+    expect(provider.maybeRotateContinuation('sess-old', CWD)).toContain('d');
+  });
+
+  it('returns null for an unknown session id', () => {
+    const provider = new ClaudeProvider();
+    expect(provider.maybeRotateContinuation('does-not-exist', CWD)).toBeNull();
+  });
+});
diff --git a/container/agent-runner/src/providers/claude.ts b/container/agent-runner/src/providers/claude.ts
index 31be51ae4..f764c7c84 100644
--- a/container/agent-runner/src/providers/claude.ts
+++ b/container/agent-runner/src/providers/claude.ts
@@ -1,4 +1,5 @@
 import fs from 'fs';
+import os from 'os';
 import path from 'path';
 
 import { query as sdkQuery, type HookCallback, type PreCompactHookInput } from '@anthropic-ai/claude-agent-sdk';
@@ -188,49 +189,122 @@ const postToolUseHook: HookCallback = async () => {
   return { continue: true };
 };
 
+/**
+ * Read a Claude transcript .jsonl, render a markdown summary, and drop it into
+ * the agent's `conversations/` folder so context survives a compaction or a
+ * session rotation. Best-effort: returns false (and logs) on any failure.
+ */
+function archiveTranscriptFile(transcriptPath: string | undefined, sessionId: string | undefined, assistantName?: string): boolean {
+  if (!transcriptPath || !fs.existsSync(transcriptPath)) {
+    log('No transcript found for archiving');
+    return false;
+  }
+
+  try {
+    const content = fs.readFileSync(transcriptPath, 'utf-8');
+    const messages = parseTranscript(content);
+    if (messages.length === 0) return false;
+
+    // Try to get summary from sessions index
+    let summary: string | undefined;
+    const indexPath = path.join(path.dirname(transcriptPath), 'sessions-index.json');
+    if (fs.existsSync(indexPath)) {
+      try {
+        const index = JSON.parse(fs.readFileSync(indexPath, 'utf-8'));
+        summary = index.entries?.find((e: { sessionId: string; summary?: string }) => e.sessionId === sessionId)?.summary;
+      } catch {
+        /* ignore */
+      }
+    }
+
+    const name = summary
+      ? summary.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/^-+|-+$/g, '').slice(0, 50)
+      : `conversation-${new Date().getHours().toString().padStart(2, '0')}${new Date().getMinutes().toString().padStart(2, '0')}`;
+
+    const conversationsDir = process.env.NANOCLAW_CONVERSATIONS_DIR || '/workspace/agent/conversations';
+    fs.mkdirSync(conversationsDir, { recursive: true });
+    const filename = `${new Date().toISOString().split('T')[0]}-${name}.md`;
+    fs.writeFileSync(path.join(conversationsDir, filename), formatTranscriptMarkdown(messages, summary, assistantName));
+    log(`Archived conversation to ${filename}`);
+    return true;
+  } catch (err) {
+    log(`Failed to archive transcript: ${err instanceof Error ? err.message : String(err)}`);
+    return false;
+  }
+}
+
 function createPreCompactHook(assistantName?: string): HookCallback {
   return async (input) => {
     const preCompact = input as PreCompactHookInput;
-    const { transcript_path: transcriptPath, session_id: sessionId } = preCompact;
-
-    if (!transcriptPath || !fs.existsSync(transcriptPath)) {
-      log('No transcript found for archiving');
-      return {};
-    }
-
-    try {
-      const content = fs.readFileSync(transcriptPath, 'utf-8');
-      const messages = parseTranscript(content);
-      if (messages.length === 0) return {};
-
-      // Try to get summary from sessions index
-      let summary: string | undefined;
-      const indexPath = path.join(path.dirname(transcriptPath), 'sessions-index.json');
-      if (fs.existsSync(indexPath)) {
-        try {
-          const index = JSON.parse(fs.readFileSync(indexPath, 'utf-8'));
-          summary = index.entries?.find((e: { sessionId: string; summary?: string }) => e.sessionId === sessionId)?.summary;
-        } catch {
-          /* ignore */
-        }
-      }
-
-      const name = summary
-        ? summary.toLowerCase().replace(/[^a-z0-9]+/g, '-').replace(/^-+|-+$/g, '').slice(0, 50)
-        : `conversation-${new Date().getHours().toString().padStart(2, '0')}${new Date().getMinutes().toString().padStart(2, '0')}`;
-
-      const conversationsDir = '/workspace/agent/conversations';
-      fs.mkdirSync(conversationsDir, { recursive: true });
-      const filename = `${new Date().toISOString().split('T')[0]}-${name}.md`;
-      fs.writeFileSync(path.join(conversationsDir, filename), formatTranscriptMarkdown(messages, summary, assistantName));
-      log(`Archived conversation to ${filename}`);
-    } catch (err) {
-      log(`Failed to archive transcript: ${err instanceof Error ? err.message : String(err)}`);
-    }
+    archiveTranscriptFile(preCompact.transcript_path, preCompact.session_id, assistantName);
     return {};
   };
 }
 
+// ── Continuation rotation (cold-resume guard) ──
+
+/**
+ * Resume cost is dominated by transcript size. Past this many bytes a fresh
+ * cold container can't reload the .jsonl before the host's 30-min idle ceiling
+ * fires, so the session is dropped and started clean. Operator-overridable.
+ */
+function transcriptRotateBytes(): number {
+  return Number(process.env.CLAUDE_TRANSCRIPT_ROTATE_BYTES) || 12 * 1024 * 1024;
+}
+
+/**
+ * Secondary age trigger, measured from the transcript's first entry. 0 (or a
+ * non-positive value) disables the age check; size alone then governs.
+ */
+function transcriptRotateAgeMs(): number {
+  const days = Number(process.env.CLAUDE_TRANSCRIPT_ROTATE_AGE_DAYS);
+  return Number.isFinite(days) && days > 0 ? days * 86_400_000 : 14 * 86_400_000;
+}
+
+function claudeProjectsDir(): string {
+  const base = process.env.CLAUDE_CONFIG_DIR || path.join(process.env.HOME || os.homedir(), '.claude');
+  return path.join(base, 'projects');
+}
+
+/**
+ * Locate the .jsonl backing a session id. The SDK names project dirs by a
+ * mangled cwd; rather than reproduce that convention we scan project dirs for
+ * `<sessionId>.jsonl` (session ids are UUIDs, so this is unambiguous).
+ */
+function findTranscriptPath(sessionId: string): string | null {
+  const projects = claudeProjectsDir();
+  let dirs: string[];
+  try {
+    dirs = fs.readdirSync(projects);
+  } catch {
+    return null;
+  }
+  for (const dir of dirs) {
+    const candidate = path.join(projects, dir, `${sessionId}.jsonl`);
+    if (fs.existsSync(candidate)) return candidate;
+  }
+  return null;
+}
+
+/** Epoch-ms of the first transcript entry, or null if unreadable. */
+function transcriptStartMs(transcriptPath: string): number | null {
+  try {
+    const fd = fs.openSync(transcriptPath, 'r');
+    try {
+      const buf = Buffer.alloc(4096);
+      const n = fs.readSync(fd, buf, 0, buf.length, 0);
+      const firstLine = buf.toString('utf-8', 0, n).split('\n', 1)[0];
+      const ts = JSON.parse(firstLine)?.timestamp;
+      const ms = ts ? Date.parse(ts) : NaN;
+      return Number.isNaN(ms) ? null : ms;
+    } finally {
+      fs.closeSync(fd);
+    }
+  } catch {
+    return null;
+  }
+}
+
 // ── Provider ──
 
 /**
@@ -277,6 +351,41 @@ export class ClaudeProvider implements AgentProvider {
     return STALE_SESSION_RE.test(msg);
   }
 
+  maybeRotateContinuation(continuation: string): string | null {
+    const transcriptPath = findTranscriptPath(continuation);
+    if (!transcriptPath) return null;
+
+    let size: number;
+    try {
+      size = fs.statSync(transcriptPath).size;
+    } catch {
+      return null;
+    }
+
+    const maxBytes = transcriptRotateBytes();
+    const startMs = transcriptStartMs(transcriptPath);
+    const ageMs = startMs === null ? 0 : Date.now() - startMs;
+    const maxAgeMs = transcriptRotateAgeMs();
+
+    let reason: string | null = null;
+    if (size > maxBytes) {
+      reason = `transcript ${(size / 1_048_576).toFixed(1)}MB > ${(maxBytes / 1_048_576).toFixed(0)}MB cap`;
+    } else if (startMs !== null && ageMs > maxAgeMs) {
+      reason = `transcript ${(ageMs / 86_400_000).toFixed(1)}d old > ${(maxAgeMs / 86_400_000).toFixed(0)}d cap`;
+    }
+    if (!reason) return null;
+
+    // Preserve a readable summary, then move the heavy .jsonl out of the
+    // resume path so the SDK starts a fresh session and the disk is reclaimed.
+    archiveTranscriptFile(transcriptPath, continuation, this.assistantName);
+    try {
+      fs.renameSync(transcriptPath, `${transcriptPath}.rotated-${Date.now()}`);
+    } catch (err) {
+      log(`Failed to move rotated transcript aside: ${err instanceof Error ? err.message : String(err)}`);
+    }
+    return reason;
+  }
+
   query(input: QueryInput): AgentQuery {
     const stream = new MessageStream();
     stream.push(input.prompt);
diff --git a/container/agent-runner/src/providers/types.ts b/container/agent-runner/src/providers/types.ts
index a6722a128..d906a8ce9 100644
--- a/container/agent-runner/src/providers/types.ts
+++ b/container/agent-runner/src/providers/types.ts
@@ -14,6 +14,21 @@ export interface AgentProvider {
    * (missing transcript, unknown session, etc.) and should be cleared.
    */
   isSessionInvalid(err: unknown): boolean;
+
+  /**
+   * Optional pre-resume maintenance. Given the stored continuation token,
+   * decide whether its backing transcript has grown too large or too old to
+   * resume cheaply. Return a non-null reason string to tell the caller to drop
+   * the continuation and start a fresh session (the provider archives any
+   * recoverable summary first); return null to keep resuming.
+   *
+   * Guards the cold-resume failure mode: a long-lived hub session accumulates
+   * days of history — including base64 image blocks the agent Read — and the
+   * SDK reloads the whole .jsonl on every resume. Past a threshold the first
+   * turn alone can exceed the host's idle ceiling, so the container is killed
+   * before it ever replies. Providers without an on-disk transcript omit this.
+   */
+  maybeRotateContinuation?(continuation: string, cwd: string): string | null;
 }
 
 /**