fix(#853): gate manager/autonomous background dispatch by runtime (#863)

* fix(#853): gate manager/autonomous bg dispatch by runtime

/gsd-manager and /gsd-autonomous --interactive dispatched Plan/Execute
via Agent(run_in_background=true). On Claude Code a backgrounded agent
has no Agent/Task tool, so it cannot spawn the nested subagents those
pipelines need — per-plan worktree-isolated executors, the plan-checker,
and the verifier. The phases reported complete but isolation and
independent verification silently never ran, even with use_worktrees /
plan_check / verifier enabled.

Both workflows now resolve the runtime (config-get runtime, default
claude) before dispatching: run plan/execute INLINE on Claude Code so
the nested pipeline runs, and background-dispatch only on runtimes where
a backgrounded agent can still nest. Mirrors execute-phase.md's existing
Codex fail-closed precedent. Reconciles the stale unconditional
background/overlap/lean-context claims elsewhere in both workflows and
in the docs. Adds a content regression test pinning the gate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* docs(#853): add changeset for runtime-gated bg dispatch

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

docs/COMMANDS.md

@@ -546,7 +546,7 @@ Interactive command center for managing multiple phases from one terminal.
 **Behavior:**
 - Dashboard of all phases with visual status indicators
 - Recommends optimal next actions based on dependencies and progress
-- Dispatches work: discuss runs inline, plan/execute run as background agents
+- Dispatches work: discuss runs inline; plan/execute run as background agents on runtimes that support nested background dispatch, or inline on Claude Code
 - Designed for power users parallelizing work across phases from one terminal
 - Supports per-step passthrough flags via `manager.flags` config (see [Configuration](CONFIGURATION.md#manager-passthrough-flags))
 

docs/FEATURES.md

@@ -1986,18 +1986,18 @@ Test suite that scans all agent, workflow, and command files for embedded inject
 
 **Flag:** `/gsd-autonomous --interactive`
 
-**Purpose:** Lean-context autonomous mode that keeps discuss-phase interactive (user answers questions) while dispatching plan and execute as background agents.
+**Purpose:** Lean-context autonomous mode that keeps discuss-phase interactive (user answers questions) while dispatching plan and execute as background agents on runtimes that support nested background dispatch; on Claude Code, plan and execute run inline to preserve worktree isolation and independent verification.
 
 **Requirements:**
 - REQ-INTERACT-01: `--interactive` MUST run discuss-phase inline with interactive questions (not auto-answered)
-- REQ-INTERACT-02: `--interactive` MUST dispatch plan-phase and execute-phase as background agents for context isolation
-- REQ-INTERACT-03: `--interactive` MUST enable pipeline parallelism — discuss Phase N+1 while Phase N builds
-- REQ-INTERACT-04: Main context MUST only accumulate discuss conversations (lean context)
+- REQ-INTERACT-02: `--interactive` MUST dispatch plan-phase and execute-phase as background agents for context isolation on runtimes where a backgrounded agent can spawn subagents; on Claude Code, plan and execute run inline
+- REQ-INTERACT-03: `--interactive` MUST enable pipeline parallelism — discuss Phase N+1 while Phase N builds (applies on runtimes that support nested background dispatch; on Claude Code, discuss does not overlap planning/execution)
+- REQ-INTERACT-04: Main context MUST only accumulate discuss conversations (lean context) on runtimes that support nested background dispatch; on Claude Code, inline plan/execute also accumulate in the main context
 
 **Process:**
 1. **Discuss inline** — Run discuss-phase in the main context with user interaction
-2. **Dispatch** — Send plan and execute to background agents with fresh context windows
-3. **Pipeline** — While background agents build Phase N, begin discussing Phase N+1
+2. **Dispatch** — On runtimes that support nested background dispatch: send plan and execute to background agents with fresh context windows. On Claude Code: run plan and execute inline.
+3. **Pipeline** — On runtimes with background dispatch: while background agents build Phase N, begin discussing Phase N+1. On Claude Code: phases run sequentially.
 
 ---
 

docs/how-to/run-phases-autonomously.md

@@ -64,8 +64,8 @@ By default, autonomous mode answers discuss questions automatically using smart
 
 In interactive mode:
 - `/gsd-discuss-phase` runs inline and waits for your answers
-- Planning and execution are dispatched as background agents so you can discuss the next phase while the current one builds
-- The main context stays lean — only discuss conversations accumulate
+- On runtimes that support nested background dispatch, planning and execution are dispatched as background agents so you can discuss the next phase while the current one builds; on Claude Code, planning and execution run inline (the next phase's discuss does not overlap)
+- The main context stays lean — only discuss conversations accumulate (on runtimes with background dispatch; on Claude Code, inline plan/execute also accumulate)
 
 ---