msd-core/gsd-core/references/workstream-flag.md

Workstream Flag (--ws)

Overview

The --ws <name> flag scopes GSD operations to a specific workstream, enabling parallel milestone work by multiple Claude Code instances on the same codebase.

Resolution Priority

1. --ws <name> flag (explicit, highest priority)
2. GSD_WORKSTREAM environment variable (per-instance)
3. Session-scoped active workstream pointer in temp storage (per runtime session / terminal)
4. .planning/active-workstream file (legacy shared fallback when no session key exists)
5. null — flat mode (no workstreams)

Why session-scoped pointers exist

The shared .planning/active-workstream file is fundamentally unsafe when multiple Claude/Codex instances are active on the same repo at the same time. One session can silently repoint another session's STATE.md, ROADMAP.md, and phase paths.

GSD now prefers a session-scoped pointer keyed by runtime/session identity (GSD_SESSION_KEY, CODEX_THREAD_ID, CLAUDE_CODE_SESSION_ID, CLAUDE_CODE_SSE_PORT, terminal session IDs, or the controlling TTY). This keeps concurrent sessions isolated while preserving legacy compatibility for runtimes that do not expose a stable session key.

Session Identity Resolution

When GSD resolves the session-scoped pointer in step 3 above, it uses this order:

1. Explicit runtime/session env vars such as GSD_SESSION_KEY, CODEX_THREAD_ID, CLAUDE_SESSION_ID, CLAUDE_CODE_SESSION_ID, CLAUDE_CODE_SSE_PORT, OPENCODE_SESSION_ID, GEMINI_SESSION_ID, CURSOR_SESSION_ID, WINDSURF_SESSION_ID, TERM_SESSION_ID, WT_SESSION, TMUX_PANE, and ZELLIJ_SESSION_NAME
2. TTY or SSH_TTY if the shell/runtime already exposes the terminal path
3. A single best-effort tty probe, but only when stdin is interactive

If none of those produce a stable identity, GSD does not keep probing. It falls back directly to the legacy shared .planning/active-workstream file.

This matters in headless or stripped environments: when stdin is already non-interactive, GSD intentionally skips shelling out to tty because that path cannot discover a stable session identity and only adds avoidable failures on the routing hot path.

Pointer Lifecycle

Session-scoped pointers are intentionally lightweight and best-effort:

• Clearing a workstream for one session removes only that session's pointer file
• If that was the last pointer for the repo, GSD also removes the now-empty per-project temp directory
• If sibling session pointers still exist, the temp directory is left in place
• When a pointer refers to a workstream directory that no longer exists, GSD treats it as stale state: it removes that pointer file and resolves to null until the session explicitly sets a new active workstream again

GSD does not currently run a background garbage collector for historical temp directories. Cleanup is opportunistic at the pointer being cleared or self-healed, and broader temp hygiene is left to OS temp cleanup or future maintenance work.

Routing Propagation

All workflow routing commands include ${GSD_WS} which:

• Expands to --ws <name> when a workstream is active
• Expands to empty string in flat mode (backward compatible)

This ensures workstream scope chains automatically through the workflow: new-milestone → discuss-phase → plan-phase → execute-phase → transition

Directory Structure

.planning/
├── PROJECT.md          # Shared
├── config.json         # Shared
├── milestones/         # Shared
├── codebase/           # Shared
├── active-workstream   # Legacy shared fallback only
└── workstreams/
    ├── feature-a/      # Workstream A
    │   ├── STATE.md
    │   ├── ROADMAP.md
    │   ├── REQUIREMENTS.md
    │   └── phases/
    └── feature-b/      # Workstream B
        ├── STATE.md
        ├── ROADMAP.md
        ├── REQUIREMENTS.md
        └── phases/

CLI Usage

# All gsd-tools query commands accept --ws
gsd-tools query state.json --ws feature-a
gsd-tools query find-phase 3 --ws feature-b

# Session-local switching without --ws on every command
GSD_SESSION_KEY=my-terminal-a gsd-tools query workstream.set feature-a
GSD_SESSION_KEY=my-terminal-a gsd-tools query state.json
GSD_SESSION_KEY=my-terminal-b gsd-tools query workstream.set feature-b
GSD_SESSION_KEY=my-terminal-b gsd-tools query state.json

# Workstream CRUD
gsd-tools query workstream.create <name>
gsd-tools query workstream.list
gsd-tools query workstream.status <name>
gsd-tools query workstream.complete <name>