Add `codex inject` to send prompts to existing sessions (automation + orchestration)

What variant of Codex are you using?

CLI

What feature would you like to see?

• Title
Add codex inject to send prompts to existing sessions (automation + orchestration)

### Summary
Please add a direct CLI command to inject a user message into an existing Codex session from outside the TUI.

Current workflow for external automation is awkward (codex resume ... "prompt").
### Core CLI Proposal
``bash
codex inject <session_name_or_id> --text "..."
`
Also accept alias:
`bash
codex inject <session_name_or_id> --text_file /path/to/prompt.txt
``

### Expected Behavior

• If the target session is running: append the message as a new user turn.

### Example Use Cases
#### End-of-Train Script
``bash
codex inject <session_name> --text "Training finished. Read logs/train.log and propose next run config."
``

#### Coder-Architect Pattern
```bash
# Architect -> Coder
codex inject <coder_session_name> --text "Implement API pagination for /v1/items and add tests."

# Coder -> Architect
codex inject <architect_session_name> --text "Implementation complete on branch feat/pagination. Review diff and propose follow-up refactors."
```

#### CI Failure Triage
``bash
codex inject <session_name> --text "CI failed on test_auth_refresh. Read latest test logs and propose minimal fix."
``

### CLI Enhancements (Future)

• --hook-name <name> for automation/audit labels.
• --text - (stdin support).
• Delivery control: --queue (default) and --interrupt.
• Session behavior flags: --resume, --create-if-missing, --if-running.
• Scriptability: --json, --wait, --timeout.
• Reliability: --idempotency-key + replay protection.
• Safety: --dry-run preflight output.
• Access/security: session ownership checks, authenticated caller checks, and encrypted local transport for injection requests.
• Optional local automation listener backend (socket/localhost port), while keeping codex inject as the primary UX.

### Scope
Cross-platform CLI feature (Linux/macOS/Windows), independent of shell or terminal multiplexer.

### Note
Drafted by Codex (AI assistant).

Additional information

_No response_