Implementation Plan: Resume Retains Selected Executable Path

Branch: t3/resume-selected-executable | Date: 2026-10-08 | Spec: spec.md

Summary

Implement a pure helper resolve_resume_argv(original_argv: &[String], resume_argv: &[String]) -> Vec<String> in signaltty-agent. Wire it into signaltty-server::router at the two session identity writers (h_hook_event, h_pane_report_session) and at resume execution (h_pane_resume).

Design & Architecture

1. Pure Helper in signaltty-agent

crates/signaltty-agent/src/resume.rs:

Rules:

1. If resume_argv is empty, return empty vector.
2. If resume_argv[0] contains / (path-qualified, e.g. explicit manifest path), return resume_argv as-is.
3. If original_argv is empty, its first path is not absolute, or the resume program is empty, return resume_argv as-is. Legacy relative paths have no reliable launch directory.
4. Extract original_basename from original_argv[0]. If original_basename == Some(resume_argv[0]): Replace argv[0] with original_argv[0], keeping resume_argv[1..].
5. Otherwise (e.g. promoted shell, wrapper with different basename), return resume_argv as-is.

2. Integration Seams in signaltty-server

• h_hook_event: When adapter.session_identity updates p.agent.resume_argv, resolve via resolve_resume_argv(&p.argv, &resume_argv).
• h_pane_report_session: When writing pane.agent.resume_argv, resolve via resolve_resume_argv(&pane.argv, &r.argv).
• h_pane_resume: When extracting raw_argv from pane.agent.resume_argv, resolve via resolve_resume_argv(&pane.argv, &raw_argv), spawn with resolved, and update pane.agent.resume_argv = Some(resolved.clone()) only after successful spawn.

TDD Plan

1. Red Test Phase:
   • Write pure unit tests in crates/signaltty-agent/src/resume.rs covering:
     • 5 built-in adapters (codex, claude, opencode, cursor, pi)
     • Relative paths (./bin/codex, sub/bin/claude)
     • Empty inputs ([], [""])
     • Bare commands (["codex"])
     • Promoted shells (["/bin/bash"])
     • Explicit manifest paths (["/manifest/bin/codex", ...])
     • Suffix flags on original command (["/opt/codex", "-m", "gpt-4"])
     • Differing wrapper basenames (["/usr/local/bin/my-wrapper"])
   • Write real IPC integration regression tests in crates/signaltty-server/tests/integration.rs:
     • Sibling test report_session_builds_resume_retains_selected_executable_without_manifest
     • Hook-event writer test
     • Stale bare snapshot repair test
   • Run tests and record RED failure output.
2. Implementation Phase:
   • Implement resolve_resume_argv and export from signaltty-agent.
   • Update h_hook_event, h_pane_report_session, and h_pane_resume in crates/signaltty-server/src/router.rs.
3. Green Test Phase:
   • Run the new unit and integration tests and verify GREEN.
   • Run clippy and fmt on signaltty-agent and signaltty-server.
4. Documentation:
   • Update docs/07-agents.md and docs/08-ipc.md.

Review follow-up: normalize relative path-qualified argv0 before spawn/split, using launch cwd under the existing Store lock, without canonicalizing symlinks or changing bare PATH commands. Await and reap the owned server via the existing wait_for_exit testkit helper before editing old snapshot fixtures.