fix(#621): route plan-phase post-planning-gaps through gsd_run launcher (#635)

* fix(#621): route plan-phase post-planning-gaps through gsd_run launcher

The post-planning-gaps step in gsd-core/workflows/plan-phase.md invoked
gsd-tools via a hardcoded `node "$HOME/.claude/gsd-core/bin/gsd-tools.cjs"`
path twice on one line — for the gap-analysis call and its nested
init.plan-phase phase_req_ids query — bypassing the gsd_run launcher that
every other call in the workflow uses. On non-default install/runtime layouts
(relocated/global installs, non-Claude runtimes) the hardcoded path does not
resolve, so the assistant reported the gap-analysis tool as "not found" and
fell back to a frontmatter-only coverage check even when a working install
existed. #3668 fixed this class earlier in the file but missed this block.

Route both invocations through gsd_run, matching the rest of the workflow.
No hardcoded $HOME gsd-tools path remains in plan-phase.md.

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

* chore(#621): add changeset for plan-phase gsd_run gap-analysis fix

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

* test(#621): update bug-2851 §13e guard for the gsd_run gap-analysis form

The #621 fix migrates plan-phase.md's post-planning-gaps gap-analysis call
from the hardcoded node "$HOME/.claude/gsd-core/bin/gsd-tools.cjs" form to the
gsd_run launcher (the canonical resolvable form every other call in the file
uses). bug-2851's §13e subtest pinned that line to the absolute-$HOME form and
now asserts stale behavior.

Update the §13e assertion to require `gsd_run gap-analysis` (still rejecting a
regression to the hardcoded $HOME path), retitle it, and note the migration in
the file header. The generic bare-`gsd-tools` sweeper test is unchanged —
gsd_run is a resolvable launcher, not a bare gsd-tools call.

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

---------

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

.changeset/curious-lynx-travel.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 635
+---
+**`/gsd-plan-phase` gap-analysis no longer reports the tool as "not found" on non-default installs** — the post-planning-gaps step now resolves `gsd-tools` through the workflow's `gsd_run` launcher instead of a hardcoded `$HOME/.claude/...` path, so it works under relocated/global installs and non-Claude runtimes instead of silently falling back to a frontmatter-only coverage check.