feat: add --terminal flag to control clientCapabilities.terminal

[DMQ]

Add a new command-line flag --terminal (default: true) that allows users to control whether the terminal capability is enabled in clientCapabilities during ACP initialization.

Usage:
acpx --terminal=false codex exec "list files"
acpx --no-terminal codex exec "list files"

Changes:

• Add terminal option to AcpClientOptions in types.ts
• Add --terminal flag to CLI in cli/flags.ts
• Pass terminal option through all session runtime functions
• Use terminal option in ACP client initialization

[dutifulbob]

Triage result

• Human attention: ⚠️ Required
• Recommendation: 🏁 escalate to a human
• Human decision needed: determine and run the appropriate targeted validation for the new --terminal/--no-terminal behavior, then make the landing decision

Quick read

This PR adds a CLI switch to control whether acpx advertises ACP terminal capability during client initialization. The solution was judged right-shaped, but this run stopped on the human handoff path because no targeted local validation command could be derived for the feature.

Intent

Give acpx users a CLI switch to turn ACP terminal support on or off, so they can run agents without exposing terminal access when they do not want it.

Underlying problem: acpx currently hardcodes clientCapabilities.terminal to true during ACP initialization, so users cannot disable terminal capability in environments or workflows where it should be hidden or unsupported.

Why

This is a feature path, not a bug-repro path. The change adds new user-facing behavior through --terminal / --no-terminal and threads that behavior through ACP initialization and session runtime code.

Targeted validation was considered necessary because the flag affects multiple runtime entry points, but the flow could not derive a concrete targeted test command. The current validation state is feature_not_validated.

Codex review

The solution was judged good_enough in shape:

• src/client.ts changes ACP initialization from a hardcoded terminal capability to a runtime-controlled value.
• src/cli/flags.ts adds the global terminal boolean and resolves --no-terminal to false.
• src/cli-core.ts, src/session-runtime.ts, and queue-owner/prompt-runner paths propagate the setting through the main execution paths.

Initial merge conflicts were detected earlier against origin/main in:

• src/session-runtime.ts
• src/session-runtime/prompt-runner.ts

No separate Codex review findings are available in this handoff state.

CI/CD

No CI/CD result is available in this handoff state.

No final conflict-gate result is available either. The current run state only records the earlier initial conflict detection plus the validation stop condition.

Recommendation

Escalate to a human.

Recommended next action: identify the correct targeted validation for the new terminal-capability flag behavior, run it, and then decide whether the PR is ready to land.