diff --git a/scripts/harness-version.json b/scripts/harness-version.json
index e225bbbad..695848771 100644
--- a/scripts/harness-version.json
+++ b/scripts/harness-version.json
@@ -38,15 +38,15 @@
     "test/helpers/pty/classify.ts": {"blob":"3f2daa12ff6484f96b8d28d910a50231c4bb3ae8","since":6},
     "test/helpers/pty/fake-session.ts": {"blob":"554e064ef259b8444280eddfe9b0db93c66a8202","since":6},
     "test/helpers/pty/judge.ts": {"blob":"81c5bb4c48ab928aca2f186a1ade9df7169d7fbe","since":6},
-    "test/helpers/pty/launch.ts": {"blob":"e4413de380b799659170e7da248d51afda3b0e3f","since":6,"nonBehavioral":"credential rejections are classed infra instead of assertion: no case's pass or fail changes; only failed trials whose provider rejected the run's key move class, so no rerun spends on a rejected key"},
+    "test/helpers/pty/launch.ts": {"blob":"d2e51418ce284815a26e174d777ca8b47ffd7e68","since":6,"nonBehavioral":"PTY sessions price their ledger row from the session transcript; the launcher pins a random --session-id (Claude otherwise picks its own random one) when the caller passes none and is not resuming; no prompt, answer, timeout or verdict changes"},
     "test/helpers/pty/plan-native.ts": {"blob":"ddba9cb68c7c0da935cff7c1cea258dee2dff740","since":6},
     "test/helpers/pty/runners/counting.ts": {"blob":"8c5c05e54abf961259d34d9c3d77db67138d7794","since":6},
     "test/helpers/pty/runners/floor.ts": {"blob":"54e2145832bb98913644d10ff303792d67f9362e","since":6,"nonBehavioral":"Removes the plan-design 0D focus picker from the shared harness; floor.ts gains an optional pickSetupChoice hook that no other caller passes, so no other case's input or verdict can change. plan-design-finding-floor, the only case whose seed raises that menu, passes the picker from its owned fixture test/fixtures/design-floor-focus-picker.ts, so its owned bytes start its own new series."},
     "test/helpers/pty/runners/observation.ts": {"blob":"1c2b75fbb984708725abaa8939125f7cab969f9f","since":6},
     "test/helpers/pty/screen.ts": {"blob":"f3743152fc9bb7a8e8c70002f75bf45914f260d5","since":6,"nonBehavioral":"credential rejections are classed infra instead of assertion: no case's pass or fail changes; only failed trials whose provider rejected the run's key move class, so no rerun spends on a rejected key"},
-    "test/helpers/pty/session.ts": {"blob":"54fe04b61d953e4e55e2fc251532c04a49fab66f","since":6,"nonBehavioral":"credential rejections are classed infra instead of assertion: no case's pass or fail changes; only failed trials whose provider rejected the run's key move class, so no rerun spends on a rejected key"},
+    "test/helpers/pty/session.ts": {"blob":"8fd1749a62f24dc37ae186c8a21c2165f7f7645e","since":6,"nonBehavioral":"PTY sessions price their ledger row from the session transcript; the launcher pins a random --session-id (Claude otherwise picks its own random one) when the caller passes none and is not resuming; no prompt, answer, timeout or verdict changes"},
     "test/helpers/session-drain-policy.ts": {"blob":"6211239dd0485e6495a700b824a7e0e61d1bcd97","since":6},
-    "test/helpers/session-ledger.ts": {"blob":"5d8b796ccd422f4e1e2ab395bf6ce5a2e4c0e167","since":6,"nonBehavioral":"Cost attribution only (GSTA-150 PR 2): a display-label record carries cost_case_id from runSkillTest's testName and the report binds its cost by it while the failed record and failure class still come from the named records (test/paid-report-cost.test.ts pins both); an aborted Agent SDK session logs its streamed usage as streamed_cost_usd, used only when a case has no record; a listed model-free case with no record or session is a known $0. No case's execution, outcome, failure class, rerun eligibility or panel verdict changes, so no pass-rate series resets"},
+    "test/helpers/session-ledger.ts": {"blob":"c99baaaa0a77a5a72384493fd8a85a4253ecb05d","since":6,"nonBehavioral":"PTY sessions price their ledger row from the session transcript; the launcher pins a random --session-id (Claude otherwise picks its own random one) when the caller passes none and is not resuming; no prompt, answer, timeout or verdict changes"},
     "test/helpers/session-runner.ts": {"blob":"c73b2596d9eb5377530a6bf1d284e0b6ea1556a0","since":6,"nonBehavioral":"Cost attribution only (GSTA-150 PR 2): a display-label record carries cost_case_id from runSkillTest's testName and the report binds its cost by it while the failed record and failure class still come from the named records (test/paid-report-cost.test.ts pins both); an aborted Agent SDK session logs its streamed usage as streamed_cost_usd, used only when a case has no record; a listed model-free case with no record or session is a known $0. No case's execution, outcome, failure class, rerun eligibility or panel verdict changes, so no pass-rate series resets"},
     "test/helpers/skill-fixture.ts": {"blob":"8a654dae6b0a396d839b02179119ae3e3bb13f69","since":6,"nonBehavioral":"extractSkillBody and extractSkillSections follow the shared-preamble hoist (pointer plus sections/preamble.md); every fixture they build is byte-identical to the pre-hoist output (compared for 8 body and 4 section extractions), so no case's input or verdict changes; the /ship review then reworded only comments and two error messages, so no fixture byte changes"},
     "test/helpers/skill-startup.ts": {"blob":"a8d21e3817c3f35a1d06af325c92fde7d420e377","since":6,"nonBehavioral":"readSkillEffective also appends a variant's added ### subsections (office-hours' Open-ended questions); readSkillStartup, readSharedSections and readSkillEffective return bytes identical to the pinned helper for every tier 2+ render without added subsections (735 across all hosts) and for office-hours' SKILL.md before this PR, so office-hours' fixture input changes only because its prompt changed in this PR, not because the helper did"},
diff --git a/test/helpers/claude-pty-runner.launch.unit.test.ts b/test/helpers/claude-pty-runner.launch.unit.test.ts
index 0f6123afe..5913435b6 100644
--- a/test/helpers/claude-pty-runner.launch.unit.test.ts
+++ b/test/helpers/claude-pty-runner.launch.unit.test.ts
@@ -39,7 +39,7 @@ describe('launchClaudePty model pin', () => {
     expect(opts.model).toBe('claude-sonnet-4-6');
   });
 
-  test.skipIf(process.platform === 'win32')('spawn args pin --model from the fallback chain, before extraArgs, with hermetic MCP gating', () => {
+  test.skipIf(process.platform === 'win32')('spawn args pin --model from the fallback chain, before extraArgs, with hermetic MCP gating and a pinned session id', () => {
     const dir = mkdtempSync(join(tmpdir(), 'pty-model-pin-'));
     try {
       const fake = join(dir, 'fake-claude');
@@ -56,7 +56,9 @@ const argv = async (opts, evalsModel) => {
 };
 process.stdout.write(JSON.stringify({ capture: resolveEvalModel('capture'),
   fallback: await argv({}, undefined), env: await argv({}, 'env-model'), explicit: await argv({ model: 'opts-model' }, 'env-model'),
-  extra: await argv({ extraArgs: ['--model', 'override'] }, undefined) }));
+  extra: await argv({ extraArgs: ['--model', 'override'] }, undefined),
+  pinned: await argv({ extraArgs: ['--session-id', '11111111-2222-4333-8444-555555555555'] }, undefined),
+  resumed: await argv({ extraArgs: ['--resume', 'prior'] }, undefined) }));
 `);
       const run = (hermetic: string) => {
         const result = spawnSync(process.execPath, [worker], { cwd: join(import.meta.dir, '../..'), encoding: 'utf8', timeout: 30_000,
@@ -73,6 +75,13 @@ process.stdout.write(JSON.stringify({ capture: resolveEvalModel('capture'),
       expect(hermetic.extra.slice(-2)).toEqual(['--model', 'override']);
       expect(hermetic.fallback).toContain('--strict-mcp-config');
       expect(run('0').fallback).not.toContain('--strict-mcp-config');
+      const sessionIds = (args: string[]) => args.flatMap((arg, i) => arg === '--session-id' ? [args[i + 1]] : []);
+      expect(sessionIds(hermetic.fallback)).toHaveLength(1);
+      expect(sessionIds(hermetic.fallback)[0]).toMatch(/^[0-9a-f]{8}(-[0-9a-f]{4}){3}-[0-9a-f]{12}$/);
+      expect(sessionIds(hermetic.extra)).toHaveLength(1);
+      expect(sessionIds(hermetic.pinned)).toEqual(['11111111-2222-4333-8444-555555555555']);
+      expect(sessionIds(hermetic.resumed)).toEqual([]);
+      expect(sessionIds(run('0').fallback)).toEqual([]);
     } finally { rmSync(dir, { recursive: true, force: true }); }
   }, 60_000);
 });
diff --git a/test/helpers/pty-transcript-cost.unit.test.ts b/test/helpers/pty-transcript-cost.unit.test.ts
new file mode 100644
index 000000000..c02e5db07
--- /dev/null
+++ b/test/helpers/pty-transcript-cost.unit.test.ts
@@ -0,0 +1,58 @@
+import { describe, test, expect } from 'bun:test';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import { pricedTranscript, ptyTranscriptCostUsd } from './pty/transcript-cost';
+
+const SID = '11111111-2222-4333-8444-555555555555';
+const assistant = (id: string, model: string, usage: object, extra: object = {}) =>
+  JSON.stringify({ type: 'assistant', sessionId: SID, message: { id, model, role: 'assistant', usage }, ...extra });
+
+function fixture(write: (project: string) => void): string {
+  const config = fs.mkdtempSync(path.join(os.tmpdir(), 'pty-cost-'));
+  const project = path.join(config, 'projects', '-fixture-cwd');
+  fs.mkdirSync(project, { recursive: true });
+  write(project);
+  return config;
+}
+
+describe('ptyTranscriptCostUsd', () => {
+  test('prices the session, its inline sidechains and subagent files, each message id once at its largest output', () => {
+    const config = fixture(project => {
+      fs.writeFileSync(path.join(project, `${SID}.jsonl`), [
+        JSON.stringify({ type: 'user', sessionId: SID, message: { role: 'user', content: 'hi' } }),
+        assistant('msg_a', 'claude-opus-5-5', { input_tokens: 1000, output_tokens: 10 }),
+        assistant('msg_a', 'claude-opus-5-5', { input_tokens: 1000, output_tokens: 500 }),
+        assistant('msg_side', 'claude-opus-5-5', { input_tokens: 0, output_tokens: 1000 }, { isSidechain: true }),
+        assistant('msg_syn', '<synthetic>', { input_tokens: 0, output_tokens: 0 }),
+        '{"partial":',
+      ].join('\n'));
+      fs.mkdirSync(path.join(project, SID, 'subagents'), { recursive: true });
+      fs.writeFileSync(path.join(project, SID, 'subagents', 'agent-x.jsonl'),
+        assistant('msg_sub', 'claude-opus-5-5', { input_tokens: 0, cache_read_input_tokens: 10000, output_tokens: 0 }) + '\n');
+      fs.writeFileSync(path.join(project, '99999999-2222-4333-8444-555555555555.jsonl'),
+        assistant('msg_foreign', 'claude-opus-5-5', { input_tokens: 1_000_000, output_tokens: 0 }) + '\n');
+    });
+    try {
+      // opus-5-5: $4 in, $20 out, $0.20 cached per MTok.
+      const expected = (1000 * 4 + 500 * 20 + 1000 * 20 + 10000 * 0.2) / 1_000_000;
+      expect(ptyTranscriptCostUsd(config, SID)).toBeCloseTo(expected, 6);
+      expect(pricedTranscript({ hermeticConfigDir: config, sessionId: SID }).streamed_cost_usd).toBeCloseTo(expected, 6);
+    } finally { fs.rmSync(config, { recursive: true, force: true }); }
+  });
+
+  test('stays cost-unknown without a transcript, a session id, usage or a priced model', () => {
+    const unpriced = fixture(project => fs.writeFileSync(path.join(project, `${SID}.jsonl`),
+      assistant('msg_a', 'claude-opus-5-5', { output_tokens: 1 }) + '\n' + assistant('msg_b', 'some-unpriced-model', { output_tokens: 1 }) + '\n'));
+    const empty = fixture(project => fs.writeFileSync(path.join(project, `${SID}.jsonl`), JSON.stringify({ type: 'user', sessionId: SID }) + '\n'));
+    try {
+      expect(ptyTranscriptCostUsd(unpriced, SID)).toBeUndefined();
+      expect(ptyTranscriptCostUsd(empty, SID)).toBeUndefined();
+      expect(ptyTranscriptCostUsd(empty, '99999999-2222-4333-8444-555555555555')).toBeUndefined();
+      expect(ptyTranscriptCostUsd(unpriced, undefined)).toBeUndefined();
+      expect(ptyTranscriptCostUsd(null, SID)).toBeUndefined();
+      expect(ptyTranscriptCostUsd(path.join(empty, 'missing'), SID)).toBeUndefined();
+      expect(pricedTranscript(undefined)).toEqual({});
+    } finally { for (const dir of [unpriced, empty]) fs.rmSync(dir, { recursive: true, force: true }); }
+  });
+});
diff --git a/test/helpers/pty/launch.ts b/test/helpers/pty/launch.ts
index e4413de38..d2e51418c 100644
--- a/test/helpers/pty/launch.ts
+++ b/test/helpers/pty/launch.ts
@@ -2,6 +2,7 @@
  * Spawn `claude` in a real PTY (launchClaudePty) and the session handle. Moved from claude-pty-runner.ts.
  * Import through test/helpers/claude-pty-runner.ts from tests; pty/ modules import siblings directly.
  */
+import { randomUUID } from 'node:crypto';
 import * as path from 'node:path';
 import { resolveEvalModel } from '../../../lib/eval-model';
 import { hermeticChildEnv, hermeticSkillsConfigDir, isHermeticEnabled } from '../hermetic-env';
@@ -15,6 +16,7 @@ import { trustDialogInput } from '../pty-trust-dialog';
 import { resolveClaudeBinary } from './binary';
 import { createPtyScreen, screenPanelEnd, stripAnsi } from './screen';
 import { appendSessionLedger, sessionKey } from '../session-ledger';
+import { pricedTranscript } from './transcript-cost';
 
 export interface ClaudePtyOptions {
   /** Register the repo's shipped skills in the child's user scope via
@@ -129,6 +131,8 @@ export interface ClaudePtySession {
    * the dir name ends in `/.claude` by contract).
    */
   hermeticConfigDir: string | null;
+  /** The Claude session id the launcher pinned (or the caller's --session-id): its transcript prices the session ledger row. */
+  sessionId?: string;
   /** Owned HOME/.gstack created by the seeded launcher; absent for caller overrides. */
   hermeticSkillStateRoot?: string;
   /** Owned pre-tool identity record, removed by close(). */
@@ -249,7 +253,8 @@ export async function launchClaudePty(
       recorded = true;
       const elapsed = performance.now() - startedMono;
       appendSessionLedger({ key: sessionKey('pty', undefined), runner: 'pty', started_at: startedAt, budget_ms: timeoutMs,
-        elapsed_ms: elapsed, end: elapsed >= timeoutMs ? 'session_timeout' : 'completed', ...screenPanelEnd(handle.visibleText()), billed: false });
+        elapsed_ms: elapsed, end: elapsed >= timeoutMs ? 'session_timeout' : 'completed', ...screenPanelEnd(handle.visibleText()), billed: false,
+        ...pricedTranscript(handle) });
     }
     return close();
   } });
@@ -263,6 +268,7 @@ interface LaunchSetup {
   hermeticSkillStateRoot: string | undefined;
   autoplanArtifactStateRoot: string | undefined;
   autoplanEngTestPlanStateRoot: string | undefined;
+  sessionId: string | undefined;
 }
 
 function prepareLaunch(opts: ClaudePtyOptions): LaunchSetup {
@@ -283,6 +289,10 @@ function prepareLaunch(opts: ClaudePtyOptions): LaunchSetup {
   // Before opts.extraArgs so a test could theoretically supply --mcp-config.
   const hermetic = isHermeticEnabled();
   if (hermetic) args.push('--strict-mcp-config');
+  const extra = opts.extraArgs ?? [];
+  const resumes = extra.some(arg => ['--resume', '-r', '--continue', '-c'].includes(arg));
+  let sessionId = extra.includes('--session-id') ? extra[extra.indexOf('--session-id') + 1] : undefined;
+  if (hermetic && !sessionId && !resumes) args.push('--session-id', sessionId = randomUUID());
   if (opts.extraArgs) args.push(...opts.extraArgs);
 
   // Hermetic by default (test/helpers/hermetic-env.ts): operator session
@@ -319,7 +329,7 @@ function prepareLaunch(opts: ClaudePtyOptions): LaunchSetup {
 
   const autoplanEngTestPlanStateRoot = opts.approveAutoplanArtifactEdits && opts.autoplanArtifactState !== undefined
     ? hermeticSkillStateRoot : undefined;
-  return { args, childEnv, hermetic, hermeticSkillStateRoot, autoplanArtifactStateRoot, autoplanEngTestPlanStateRoot };
+  return { args, childEnv, hermetic, hermeticSkillStateRoot, autoplanArtifactStateRoot, autoplanEngTestPlanStateRoot, sessionId };
 }
 
 interface LaunchRecorders {
@@ -568,6 +578,7 @@ function sessionHandle(pty: PtyProcess, launch: LaunchSetup, wallTimer: ReturnTy
     exited: () => pty.exited,
     exitCode: () => pty.exitCode,
     hermeticConfigDir: launch.hermetic ? launch.childEnv.CLAUDE_CONFIG_DIR ?? null : null,
+    sessionId: launch.sessionId,
     hermeticSkillStateRoot: launch.hermeticSkillStateRoot,
     pendingPlanReadyFile: pendingExit?.file,
     pendingQuestionFile: pendingQuestion?.file,
diff --git a/test/helpers/pty/session.ts b/test/helpers/pty/session.ts
index 54fe04b61..8fd1749a6 100644
--- a/test/helpers/pty/session.ts
+++ b/test/helpers/pty/session.ts
@@ -10,6 +10,7 @@
 import { launchClaudePty, type ClaudePtyOptions, type ClaudePtySession } from './launch';
 import { screenPanelEnd } from './screen';
 import { appendSessionLedger, sessionKey, type SessionEnd } from '../session-ledger';
+import { pricedTranscript } from './transcript-cost';
 
 /**
  * The runners' launch seam: how a session starts, and the clock the runner
@@ -97,7 +98,7 @@ export async function runPtySession<R>(plan: PtySessionPlan<R>): Promise<R> {
   } finally {
     appendSessionLedger({ key: sessionKey('pty', undefined), runner: 'pty', started_at: startedAt,
       budget_ms: plan.budgetMs ?? plan.launch.timeoutMs ?? 240_000, elapsed_ms: plan.driver.monotonic() - started,
-      end, ...safePanelEnd(session), billed: false });
+      end, ...safePanelEnd(session), billed: false, ...pricedTranscript(session) });
     try {
       try { plan.beforeClose?.(session, failure); }
       catch (error) { if (!failure) { failure = { error }; throw error; } }
diff --git a/test/helpers/pty/transcript-cost.ts b/test/helpers/pty/transcript-cost.ts
new file mode 100644
index 000000000..064d520b8
--- /dev/null
+++ b/test/helpers/pty/transcript-cost.ts
@@ -0,0 +1,42 @@
+import * as fs from 'node:fs';
+import * as path from 'node:path';
+import { streamedUsageCostUsd } from '../../../lib/pricing';
+
+/** The session ledger's cost field for a PTY session: present only when its transcript prices. */
+export function pricedTranscript(session: { hermeticConfigDir?: string | null; sessionId?: string } | undefined): { streamed_cost_usd?: number } {
+  const cost = ptyTranscriptCostUsd(session?.hermeticConfigDir, session?.sessionId);
+  return cost === undefined ? {} : { streamed_cost_usd: cost };
+}
+
+/**
+ * Price one PTY session from the transcripts Claude Code wrote under its owned config dir:
+ * `projects/<dir>/<sessionId>.jsonl` (inline sidechains included) and `projects/<dir>/<sessionId>/subagents/*.jsonl`,
+ * rows deduplicated by message id. Undefined (cost-unknown, never $0) without a config dir, session id, transcript or
+ * usage, or when a message's model has no price row.
+ */
+export function ptyTranscriptCostUsd(configDir: string | null | undefined, sessionId: string | undefined): number | undefined {
+  if (!configDir || !sessionId) return undefined;
+  const projects = path.join(configDir, 'projects');
+  let dirs: fs.Dirent[];
+  try {
+    dirs = fs.readdirSync(projects, { withFileTypes: true });
+  } catch {
+    return undefined;
+  }
+  const files: string[] = [];
+  for (const dir of dirs) {
+    if (!dir.isDirectory()) continue;
+    const main = path.join(projects, dir.name, `${sessionId}.jsonl`);
+    if (fs.existsSync(main)) files.push(main);
+    const subagents = path.join(projects, dir.name, sessionId, 'subagents');
+    if (fs.existsSync(subagents)) files.push(...fs.readdirSync(subagents).filter(f => f.endsWith('.jsonl')).map(f => path.join(subagents, f)));
+  }
+  const rows = files.flatMap(file => fs.readFileSync(file, 'utf8').split('\n').flatMap(line => {
+    try {
+      return [JSON.parse(line)];
+    } catch {
+      return [];
+    }
+  }));
+  return streamedUsageCostUsd(rows);
+}
diff --git a/test/helpers/session-ledger.ts b/test/helpers/session-ledger.ts
index 5d8b796cc..c99baaaa0 100644
--- a/test/helpers/session-ledger.ts
+++ b/test/helpers/session-ledger.ts
@@ -52,7 +52,7 @@ export interface SessionLedgerRow {
   liveness?: LivenessSummary;
   /** Whether the runner captured this session's billing (a terminal result with total_cost_usd). */
   billed?: boolean;
-  /** A session that ended without a terminal result (aborted, thrown): its assistant messages' streamed usage at lib/pricing.ts rates, absent when unpriced. */
+  /** A session without a terminal result (an aborted Agent SDK session, a PTY session): its assistant messages' usage at lib/pricing.ts rates, from the stream or the PTY transcript; absent when unpriced. */
   streamed_cost_usd?: number;
   /** Codex sessions: the model, its billed cost and token classes. */
   model?: string;