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

Workstream Flag (--ws)

Overview

The --ws <name> flag scopes MSD 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. MSD_WORKSTREAM environment variable (per-instance)
3. Session-scoped active workstream pointer in temp storage (per runtime session / terminal), when that pointer exists and is non-blank
4. .planning/active-workstream file — consulted whenever step 3 has nothing to say: either there is no session identity at all, or there is one but it has never pointed at a workstream. A session that already has its own pointer (step 3) is never overridden by this step, even if that pointer is stale.
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.

MSD now prefers a session-scoped pointer keyed by runtime/session identity (MSD_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.

A session that has never set its own pointer inherits .planning/active-workstream (step 4) rather than silently falling back to flat mode — this does not weaken the isolation guarantee above: inheritance only fires when a session's own pointer is absent, and a session that has ever set one is never repointed by the shared file.

Session Identity Resolution

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

1. Explicit runtime/session env vars such as MSD_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, MSD 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, MSD 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. This returns that session to step 4 of Resolution Priority above — it goes back to inheriting .planning/active-workstream (if a marker exists there), not to flat mode. A cleared session with no marker present resolves to null; a cleared session with a marker present resolves to whatever that marker names. To force flat mode for a cleared session, remove the shared marker file, or use an explicit override such as --ws / MSD_WORKSTREAM on the command in question.
• If that was the last pointer for the repo, MSD 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, MSD treats it as stale state: it removes that pointer file and resolves to null until the session explicitly sets a new active workstream again

MSD 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 ${MSD_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   # Shared marker; inherited when a session has no pointer of its own
└── 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 msd_run query commands accept --ws
msd_run query state.json --ws feature-a
msd_run query find-phase 3 --ws feature-b

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

# Workstream CRUD
msd_run query workstream.create <name>
msd_run query workstream.list
msd_run query workstream.status <name>
msd_run query workstream.complete <name>