Wire the Codex turn-flip hooks (M3.6: completes the AgentCLI seam)

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Completes the Codex adapter (ADR 0014, ROADMAP M3.6) by filling the last two hook seam stubs, so a codex task tracks the agent↔user turn ball exactly like a claude task.

What changed

• CodexAgentCLI.write_settings now merges codex's [hooks] block into config.toml (the [[hooks.Stop]] → [[hooks.Stop.hooks]] {type="command", command=…} shape), wiring the two turn-flip events to the shared, already-CLI-agnostic callback python -m panopticon.container.hook:
  • Stop → hook user stop — hands the turn to the user, guarded by the background-task check; the callback prints nothing on this path, satisfying codex's "plain-text stdout invalid for Stop" rule.
  • UserPromptSubmit → hook agent prompt — takes the turn back and prints the phase briefing + provisioning nudge.
• CodexAgentCLI.has_live_background_task parses the Stop payload (mirrors the claude adapter's err-toward-live logic).
• The block merges read-modify-write, coexisting with the MCP / trust / overview keys already in config.toml.

ADR 0014 flags resolved against codex's real hooks schema

• Flag 6 (yes): codex feeds a UserPromptSubmit hook's stdout back as developer context, so the briefing + provisioning nudge ride the same channel claude uses — no alternate channel needed.
• Flag 2: codex's Stop payload carries no background_tasks array (fields are session_id/transcript_path/cwd/hook_event_name/model/permission_mode/turn_id/stop_hook_active/last_assistant_message), so the flip degrades to the plain hand-back — claude's exact behaviour when the field is absent. The parser still lights up if a future codex build adds the field.
• Flag 7: codex has no AskUserQuestion tool, and Stop/UserPromptSubmit take no matcher, so we wire no PreToolUse/PostToolUse pair — the "agent is asking" turn state stays on the agent until the next Stop (accepted documented degradation).

Scope

The hook callback (container/hook.py) was already CLI-agnostic (resolves the adapter, calls read_hook_payload/has_live_background_task), so there is no control-plane change — the work is confined to the codex adapter and its test. Docs updated: ADR 0014 flags 2/6/7 marked resolved, AGENTS.md module map, and the shared callback comment.