feat: skill prefix is now a persistent user choice (v0.12.11.0) (#571)

* feat: make skill prefix a persistent, interactive user setting

- Add --prefix flag alongside --no-prefix
- Read/write skill_prefix from ~/.gstack/config.yaml (true/false)
- Interactive prompt on first setup when no preference saved
- Non-TTY environments default to flat names (no prefix)
- Add cleanup_prefixed_claude_symlinks() for reverse direction
- Fix gstack-config sed portability (mktemp+mv instead of BSD sed -i '')
- Add SKILL_PREFIX to preamble output with namespace-aware instruction

* test: add prefix config tests + README switching instructions

8 structural tests for persistent prefix setting:
config reading, --prefix flag, config persistence, interactive
prompt, TTY fallback, reverse cleanup, cleanup ordering, welcome.

* chore: regenerate SKILL.md files with SKILL_PREFIX preamble

* chore: bump version and changelog (v0.12.11.0)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: reframe changelog as feature, not mea culpa

* docs: update CONTRIBUTING + CLAUDE.md for prefix-aware vendoring

- CONTRIBUTING: vendoring now includes ./setup step for per-skill symlinks
- CONTRIBUTING: prefix choice documented in contributor workflow + dev diagram
- CONTRIBUTING: switching prefix mode section added
- CLAUDE.md: vendored symlink awareness section covers prefix setting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

codex/SKILL.md

@@ -33,8 +33,10 @@ _PROACTIVE=$(~/.claude/skills/gstack/bin/gstack-config get proactive 2>/dev/null
 _PROACTIVE_PROMPTED=$([ -f ~/.gstack/.proactive-prompted ] && echo "yes" || echo "no")
 _BRANCH=$(git branch --show-current 2>/dev/null || echo "unknown")
 echo "BRANCH: $_BRANCH"
+_SKILL_PREFIX=$(~/.claude/skills/gstack/bin/gstack-config get skill_prefix 2>/dev/null || echo "false")
 echo "PROACTIVE: $_PROACTIVE"
 echo "PROACTIVE_PROMPTED: $_PROACTIVE_PROMPTED"
+echo "SKILL_PREFIX: $_SKILL_PREFIX"
 source <(~/.claude/skills/gstack/bin/gstack-repo-mode 2>/dev/null) || true
 REPO_MODE=${REPO_MODE:-unknown}
 echo "REPO_MODE: $REPO_MODE"
@@ -58,6 +60,11 @@ types (e.g., /qa, /ship). If you would have auto-invoked a skill, instead briefl
 "I think /skillname might help here — want me to run it?" and wait for confirmation.
 The user opted out of proactive behavior.
 
+If `SKILL_PREFIX` is `"true"`, the user has namespaced skill names. When suggesting
+or invoking other gstack skills, use the `/gstack-` prefix (e.g., `/gstack-qa` instead
+of `/qa`, `/gstack-ship` instead of `/ship`). Disk paths are unaffected — always use
+`~/.claude/skills/gstack/[skill-name]/SKILL.md` for reading skill files.
+
 If output shows `UPGRADE_AVAILABLE <old> <new>`: read `~/.claude/skills/gstack/gstack-upgrade/SKILL.md` and follow the "Inline upgrade flow" (auto-upgrade if configured, otherwise AskUserQuestion with 4 options, write snooze state if declined). If `JUST_UPGRADED <from> <to>`: tell user "Running gstack v{to} (just updated!)" and continue.
 
 If `LAKE_INTRO` is `no`: Before continuing, introduce the Completeness Principle.