Fix codex orch send submission by using C-m

[proboscis]

Summary

• Fix orch send for codex tmux runs by using agent-specific submit key handling.
• Keep send flow as: literal message first, then submit key.
• Use C-m (carriage return) for codex; keep Enter for all other agents.
• Add unit coverage for submit-key selection.

Changes

• internal/daemon/socket.go
  • processSendTmux now always calls SendKeysLiteral first.
  • Submit key is chosen by new helper tmuxSubmitKeyForAgent(agentName).
  • Codex => C-m; others => Enter.
• internal/daemon/socket_test.go
  • Added TestTmuxSubmitKeyForAgent with codex/case-insensitive/non-codex cases.

Acceptance Criteria Evidence

1) orch send for codex submits the message

Executed from this branch binary with isolated daemon runtime + tmux wrapper:

go run ./cmd/orch send 61eb36 "ACPT-CODEX-SEND-1770743845"
# Sent message to orch-432#20260211-011850

Wrapper-captured tmux args from daemon:

send-keys -t run-orch-432-20260211-011850 -l ACPT-CODEX-SEND-1770743845
send-keys -t run-orch-432-20260211-011850 C-m

Pane capture shows the marker was actually submitted and answered:

› ACPT-CODEX-SEND-1770743845
• ACPT-CODEX-SEND-1770743845

2) Verified codex submit key sequence

Live codex pane test on tmux session:

After Enter:

› ACPT-KEYSEQ-1770743925

(message remains in input)

After C-m:

› ACPT-KEYSEQ-1770743925
• ACPT-KEYSEQ-1770743925

(submitted and processed)

3) Non-codex tmux agents unchanged

• Unit test asserts fallback remains Enter for non-codex:
  • go test ./internal/daemon -run TestTmuxSubmitKeyForAgent
• Existing tmux default behavior still validated:
  • go test ./internal/multiplexer -run TestTmuxMultiplexer_SendKeys

4) Added test

• Added TestTmuxSubmitKeyForAgent in internal/daemon/socket_test.go.

Validation Run

• go build ./... ✅
• go test ./... ❌ (pre-existing unrelated failure)
  • internal/cli/run_test.go:344 TestApplyConfigDefaultsFallbacks
  • invalid config schema ... EOF
• make lint ✅

Refs: orch-436