fix: treat direct worktree skill invocation as consent (PRI-974)

The skill previously required an explicit reply to its "do you want a
worktree?" dialogue, which produced obtuse UX when the user invoked the
skill by name — agents had to stop and ask "do you want a worktree?"
even though the user just asked for the skill whose purpose is worktrees.

Loosen Step 2 to recognize the invoking turn as consent: if the user's
most recent message named the skill, asked for a worktree, or asked for
an isolated workspace, proceed directly to Step 3 without re-prompting.
The gate still fires for the transitive case (agent infers isolation
from a feature description) — that remains the #991 failure mode.

Also trim "or skill invocation" from the anti-inference Red Flag and
destale the Integration section now that SDD/executing-plans no longer
require a worktree.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/using-git-worktrees/SKILL.md

@@ -48,7 +48,9 @@ echo "Current branch: $BRANCH"
 echo "Repository: $(basename "$(git rev-parse --show-toplevel)")"
 ```
 
-Tell the user their options, then **wait for a reply**:
+**Check the user's most recent message first.** If they already asked for a worktree, named the worktree skill, or asked for an isolated workspace in the message that invoked you, that IS the explicit ask — proceed directly to Step 3 without re-prompting.
+
+Otherwise, tell the user their options and **wait for a reply**:
 
 > "You're on `<branch>` in `<repo>`. I can set up an isolated worktree, or we can work directly here. What do you prefer?"
 
@@ -241,7 +243,7 @@ Ready to implement <feature-name>
 - Create worktree without verifying it's ignored (project-local)
 - Skip baseline test verification
 - Proceed with failing tests without asking
-- Infer worktree consent from the task description, plan, or skill invocation — only an explicit user reply counts
+- Infer worktree consent from the task description or plan — only an explicit user request counts
 
 **Always:**
 - Run Step 1 detection first
@@ -256,9 +258,9 @@ Ready to implement <feature-name>
 ## Integration
 
 **Called by:**
-- **subagent-driven-development** - Ensures isolated workspace (creates one or verifies existing)
-- **executing-plans** - Ensures isolated workspace (creates one or verifies existing)
-- Any skill needing isolated workspace
+- **subagent-driven-development** - Calls this to detect the workspace and optionally set up worktree isolation on request
+- **executing-plans** - Calls this to detect the workspace and optionally set up worktree isolation on request
+- Any skill that may use worktree isolation
 
 **Pairs with:**
 - **finishing-a-development-branch** - REQUIRED for cleanup after work complete