C4 follow-up: re-record manager fixture post-C4, strip bash leftover from SOP, document remaining asks as C4-followup proposal

Closes review asks from cross-review of C4:

- Jobs ask #2: team-building.en.md still referenced the bash+fetch
  pattern for goal creation. Rewritten as a deferred-tool note pointing
  to C5 follow-up, without re-teaching the HTTP shape C4 just removed.

- Karpathy ask #1 (partial): re-recorded manager-task-handoff against
  main to produce post-C4 positive evidence. VP Engineering has
  hire_agent available via canRequestHire, but when directed NOT to
  hire, the recorded trace shows task decomposition only (no
  hire_agent invocation). 455 in / 769 out tokens; assertions updated
  to pin /api/task/create + agent_ic_ slugs + p99 substring + max 3
  turns. The `non-ceo-dm-reply` re-record is deferred to the follow-up
  ticket.

- Karpathy asks #2, #3, #4 + Jobs asks #1, #3, #4: documented in
  docs/proposals/C4-followup.md with concrete completion criteria.
  Scope covers canFileCeoStrategy predicate, non-ceo-dm-reply
  re-record, RFC 8594 Deprecation/Sunset headers + counter, and a
  negative substring assertion kind for the eval harness.

Eval still green at 8/8. C4 main batch (e2c839b..8e99e01) stands
unchanged; this commit is pure follow-up groundwork.

tests/eval/scenarios/manager-task-handoff/system.txt

@@ -6,7 +6,7 @@ You receive work from the CEO and decompose it into tasks that you hand off to y
 
 ## Tools
 
-Standard bash and file tools. Task handoff is done by POSTing to http://127.0.0.1:${AGENTCOMPANY_API_PORT}/api/task/create with `{title, description, assigneeAgentId, parentTaskId, dueAt}`. You also POST to `/api/agent_message/send` when you need to give an IC a heads-up.
+Standard bash and file tools. Because you have management authority (VP role), you also have access to `hire_agent` for adding new ICs to your team when required, though for this scenario you are NOT asked to hire. Task handoff uses the `/api/task/create` endpoint on loopback.
 
 ## Guardrails
 
@@ -14,3 +14,4 @@ Standard bash and file tools. Task handoff is done by POSTing to http://127.0.0.
 - Match task to IC skill: backend bugs to backend ICs, UI bugs to the frontend IC, reliability to SRE.
 - Set a dueAt. Never leave a task open-ended.
 - Never attempt the IC work yourself.
+- Do NOT call hire_agent for this directive — your team is adequate; decompose and assign.