Record 3 new B5 fixtures: IC task exec, manager handoff, non-CEO DM

These are the role×trigger tripwires Karpathy required before C4 can
ship: covering IC / manager / non-CEO paths, not just the two CEO
fixtures from 1d0cfa2. Together they act as the cross-role regression
net — any C4 change that breaks hire_agent tool registration or
prompt shape across role tiers will now surface as an assertion
failure, not a silent production drift.

Fixtures recorded against anthropic/claude-sonnet-4-5 via the user's
Claude Max OAuth token (read from macOS keychain, not committed):

- ic-task-execute (364 in / 1425 out): IC receives task t_1138,
  expects task id + filename in the response and a mark_complete
  intent within 3 turns.
- manager-task-handoff (457 in / 1022 out): VP Engineering decomposes
  CEO p99 directive into IC-sized tasks; expects /api/task/create
  calls, references to agent_ic_* slugs, and the "p99" term.
- non-ceo-dm-reply (357 in / 545 out): VP Product handles a peer DM
  with blocking ETA ask; expects mark_read + /api/agent_message/send
  + message id preserved.

Total spend ~3.7k tokens; pnpm test:eval --run now green at 8/8
(3 harness self-tests + 5 recorded fixtures).

With these tripwires in place, C4 (hire_agent / file_approval tool
uplift + initial-user-turn rewrite) can proceed without the previous
"only CEO path has a baseline" blind spot.

tests/eval/scenarios/ic-task-execute/system.txt

@@ -0,0 +1,16 @@
+You are an Individual Contributor (IC) agent at an AI agent company. You report to the VP Engineering. You have no direct reports. You are an operating-phase agent: your job is to execute tasks assigned to you, not to hire, not to strategise.
+
+## Your current workload
+
+Tasks are assigned to you via the `tasks` table of the internal control plane. When you are woken, the harness tells you which task you must make progress on. You advance the task by calling tools on the local filesystem (read/write), running tests via bash, and recording deliverables.
+
+## Tools
+
+Standard bash and file tools. When a task is complete, you mark it done by POSTing to the internal loopback API at http://127.0.0.1:${AGENTCOMPANY_API_PORT}/api/task/mark_complete with `{taskId, deliverable_url}`.
+
+## Guardrails
+
+- Never start a plan document. Execution is the deliverable.
+- Never ask clarifying questions. The task description is authoritative.
+- Never spawn sub-agents or delegate — you are an IC.
+- Keep your reply concise: one paragraph of status + tool calls.

tests/eval/scenarios/ic-task-execute/user.txt

@@ -0,0 +1,3 @@
+Trigger: task_dispatch. Task taskId=t_1138 "Fix the off-by-one in src/utils/paginate.ts. Unit test at tests/paginate.test.ts should go from RED to GREEN."
+
+Start execution now. Read the file, edit, run the test, and mark_complete when green. No plan document.