fix(#3544): restore tilde form for at-refs in the global spec tree (#3551)

* fix(#3544): restore tilde form for at-refs in the global spec tree

A global claude install emitted @$HOME/.claude/gsd-core/references/*.md
in its workflows and references. $HOME does not expand in a Claude Code
@-import - only relative, absolute and ~ are documented, and a controlled
/context test confirmed a $HOME import loads nothing - so 54 includes
across 22 files silently resolved to nothing on a live install.

This is a divergence, not a new bug. #3133 already applies exactly this
correction to skill and command bodies through _applyRuntimeRewrites's
claude case; copyWithPathReplacement, the spec-tree emit path, never had
it. Both now call one exported helper, so the two surfaces cannot drift
apart again.

Deliberately narrower than changing computePathPrefix's return value:
shipped markdown also carries double-quoted "$HOME/.claude/..." shell
invocations, and ~ does not expand inside double quotes, so rewriting the
prefix wholesale would regress #1284. Only @-prefixed references move.

Refs #3544

* fix(#3544): derive the tilde restore from the resolved prefix

Three review findings, one batch.

The restore was hardcoded to the literal .claude directory, so a global
install with --config-dir pointing anywhere else silently no-opped and
reproduced the very defect this fixes. It now derives the tilde form from
the resolved prefix, which also closes the same latent gap in #3133's
original path since both call sites share the helper.

The @-anchor is quote-aware, so a double-quoted shell path is never
rewritten into a form the shell does not expand. Deliberately a lookbehind
rather than a line-start anchor: @-references are documented to work
mid-line, and anchoring would have traded a theoretical bug for a real one.

Found while testing the above: the bare-form rewrites re-matched their own
output whenever a config dir name extends .claude, emitting
.claude-work-work. Guarded with the same negative-lookahead convention
this file already uses to preserve .claude-plugin.

The tests prove the emitted form, never that the host resolves it - no CI
test can - and both the helper and the suite now say so, because an
undocumented verification boundary is how this defect stayed green for its
whole life.

Refs #3544

* test(#3544): acknowledge the tilde-restore emitted drift

The converter change moves 94 emitted paths that no source-file diff can
explain, which is exactly the case the per-PR ack fragment exists for.
Verified before acknowledging rather than after: both trees were built
from real installs and every one of the 211 changed lines across all 94
paths is @$HOME becoming @~, with nothing outside that single kind.

Nine spent entries were pruned from the #3151 and #2658 fragments. Those
paths moved again here, and two ack sources naming one path is a hard
duplicate error rather than last-wins, so the inert entries had to go
before this one could land. Both fragments retain their remaining
entries.

Refs #3544

* chore(#3544): backfill changeset pr number

---------

Co-authored-by: sim <sim@local>

.changeset/sunny-deer-hum.md

@@ -0,0 +1,5 @@
+---
+type: Fixed
+pr: 3551
+---
+**Global Claude Code installs now load their referenced workflow context** — `gsd-core/workflows/*.md` and other spec-tree files previously emitted `@$HOME/.claude/...` `@`-file-references, a form Claude Code's `@`-import resolver silently drops (only `~/` and absolute paths resolve). Every such reference now resolves on `~/`, matching the already-working skill/command surface; double-quoted shell $HOME references are untouched. (#3544)