diff --git a/scripts/resolvers/runtime-root.ts b/scripts/resolvers/runtime-root.ts
index 9617e606b..ff0044fc7 100644
--- a/scripts/resolvers/runtime-root.ts
+++ b/scripts/resolvers/runtime-root.ts
@@ -70,7 +70,7 @@ export function skillStartLines(ctx: TemplateContext): { lookup: string; command
   }
   return {
     lookup: [
-      `[ -d "\${GSTACK_ROOT:-/-}/bin" ]&&[ -d "$GSTACK_ROOT/lib" ]||GSTACK_ROOT=$(git rev-parse --show-toplevel 2>/dev/null)/${getHostConfig(ctx.host).localSkillRoot}`,
+      `[ -d "\${GSTACK_ROOT:-/-}/lib" ]&&[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=$(git rev-parse --show-toplevel 2>/dev/null)/${getHostConfig(ctx.host).localSkillRoot}`,
       `[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=${globalRoot(ctx)}`,
       `[ -d "$GSTACK_ROOT/bin" ]||echo "gstack: no install found (tried $GSTACK_ROOT). ${fix}">&2`,
     ].join('\n'),
diff --git a/test/fixtures/golden/agy-ship-SKILL.md b/test/fixtures/golden/agy-ship-SKILL.md
index b3aa51ef4..1f64ff199 100644
--- a/test/fixtures/golden/agy-ship-SKILL.md
+++ b/test/fixtures/golden/agy-ship-SKILL.md
@@ -17,9 +17,10 @@ This skill follows gstack shared preamble `6872f1ec4eb9` (AskUserQuestion format
 ## Preamble (run first)
 
 ```bash
-[ -d "${GSTACK_ROOT:-/-}/bin" ]&&[ -d "$GSTACK_ROOT/lib" ]||{ _r=$(git rev-parse --show-toplevel 2>/dev/null)/.agents/skills/gstack;[ -d "$_r/bin" ]||_r=~/.gemini/antigravity-cli/skills/gstack;[ -d "$_r/bin" ]||{ echo "gstack: no install found (tried $_r). Fix: ./setup --host agy from your gstack checkout; ./setup --status shows it.">&2;exit 1;};GSTACK_ROOT=$_r;}
-GSTACK_BIN=$GSTACK_ROOT/bin
-"$GSTACK_BIN/gstack-skill-start" --skill "ship" --model "gemini"
+[ -d "${GSTACK_ROOT:-/-}/lib" ]&&[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=$(git rev-parse --show-toplevel 2>/dev/null)/.agents/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=~/.gemini/antigravity-cli/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||echo "gstack: no install found (tried $GSTACK_ROOT). Fix: ./setup --host agy from your gstack checkout; ./setup --status shows it.">&2
+"$GSTACK_ROOT/bin/gstack-skill-start" --skill "ship" --model "gemini"
 ```
 
 **Antigravity tool names:** `AskUserQuestion` means your `ask_question` tool (options as choices); there is no `mcp__*__AskUserQuestion` variant. The Bash tool means `run_command`, the Read tool `view_file`, the Write tool `write_to_file`, the Edit tool `replace_file_content` (`multi_replace_file_content` for several edits in one file), Grep `grep_search`, Glob `find_by_name`, and the Agent tool `invoke_subagent`. There is no Skill tool: load a skill by reading its SKILL.md with `view_file`. If a step says to call `ExitPlanMode`, tell the user the plan is ready and wait. `view_file` can return only part of a long file: when a SKILL.md or a file it tells you to read ends before its last line, read the remaining line ranges before acting on it.
diff --git a/test/fixtures/golden/codex-ship-SKILL.md b/test/fixtures/golden/codex-ship-SKILL.md
index e3b16338d..019c9e671 100644
--- a/test/fixtures/golden/codex-ship-SKILL.md
+++ b/test/fixtures/golden/codex-ship-SKILL.md
@@ -17,9 +17,10 @@ This skill follows gstack shared preamble `2af24c2d75e4` (AskUserQuestion format
 ## Preamble (run first)
 
 ```bash
-[ -d "${GSTACK_ROOT:-/-}/bin" ]&&[ -d "$GSTACK_ROOT/lib" ]||{ _r=$(git rev-parse --show-toplevel 2>/dev/null)/.agents/skills/gstack;[ -d "$_r/bin" ]||_r=${CODEX_HOME:-~/.codex}/skills/gstack;[ -d "$_r/bin" ]||{ echo "gstack: no install found (tried $_r). Fix: ./setup --host codex from your gstack checkout; ./setup --status shows it.">&2;exit 1;};GSTACK_ROOT=$_r;}
-GSTACK_BIN=$GSTACK_ROOT/bin
-"$GSTACK_BIN/gstack-skill-start" --skill "ship" --model "gpt"
+[ -d "${GSTACK_ROOT:-/-}/lib" ]&&[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=$(git rev-parse --show-toplevel 2>/dev/null)/.agents/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=${CODEX_HOME:-~/.codex}/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||echo "gstack: no install found (tried $GSTACK_ROOT). Fix: ./setup --host codex from your gstack checkout; ./setup --status shows it.">&2
+"$GSTACK_ROOT/bin/gstack-skill-start" --skill "ship" --model "gpt"
 ```
 
 Read the echoed `KEY: value` STATUS lines — they drive every preamble rule
diff --git a/test/fixtures/golden/factory-ship-SKILL.md b/test/fixtures/golden/factory-ship-SKILL.md
index 148a7b6fb..981464983 100644
--- a/test/fixtures/golden/factory-ship-SKILL.md
+++ b/test/fixtures/golden/factory-ship-SKILL.md
@@ -19,9 +19,10 @@ This skill follows gstack shared preamble `99cd6cb5d373` (AskUserQuestion format
 ## Preamble (run first)
 
 ```bash
-[ -d "${GSTACK_ROOT:-/-}/bin" ]&&[ -d "$GSTACK_ROOT/lib" ]||{ _r=$(git rev-parse --show-toplevel 2>/dev/null)/.factory/skills/gstack;[ -d "$_r/bin" ]||_r=~/.factory/skills/gstack;[ -d "$_r/bin" ]||{ echo "gstack: no install found (tried $_r). Fix: ./setup --host factory from your gstack checkout; ./setup --status shows it.">&2;exit 1;};GSTACK_ROOT=$_r;}
-GSTACK_BIN=$GSTACK_ROOT/bin
-"$GSTACK_BIN/gstack-skill-start" --skill "ship" --model "claude"
+[ -d "${GSTACK_ROOT:-/-}/lib" ]&&[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=$(git rev-parse --show-toplevel 2>/dev/null)/.factory/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||GSTACK_ROOT=~/.factory/skills/gstack
+[ -d "$GSTACK_ROOT/bin" ]||echo "gstack: no install found (tried $GSTACK_ROOT). Fix: ./setup --host factory from your gstack checkout; ./setup --status shows it.">&2
+"$GSTACK_ROOT/bin/gstack-skill-start" --skill "ship" --model "claude"
 ```
 
 Read the echoed `KEY: value` STATUS lines — they drive every preamble rule
diff --git a/test/fixtures/skill-md-size-allowlist.json b/test/fixtures/skill-md-size-allowlist.json
index 45435e0a9..db541ccaf 100644
--- a/test/fixtures/skill-md-size-allowlist.json
+++ b/test/fixtures/skill-md-size-allowlist.json
@@ -2,56 +2,56 @@
   "_comment": "Generated SKILL.md files over the limit, pinned at their exact character count (#3199). test/skill-md-size-guard.test.ts fails when a pinned skill grows past its pin or shrinks below it: lower the pin when a skill shrinks and delete it once the skill is within the limit. Raising a pin is an owner decision. The shared-preamble hoist (GSTA-96) moved every tier 2+ skill's shared preamble into sections/preamble.md; the pins below are what remains.",
   "limit": 100000,
   "pins": {
-    "agy/gstack-autoplan": 109666,
-    "agy/gstack-plan-design-review": 109116,
-    "agy/gstack-plan-devex-review": 114958,
-    "agy/gstack-plan-eng-review": 143590,
-    "agy/gstack-review": 104276,
-    "codex/gstack-autoplan": 108409,
-    "codex/gstack-plan-design-review": 110473,
-    "codex/gstack-plan-devex-review": 116466,
-    "codex/gstack-plan-eng-review": 144755,
-    "codex/gstack-review": 103799,
-    "copilot/gstack-autoplan": 109109,
-    "copilot/gstack-plan-design-review": 109382,
-    "copilot/gstack-plan-devex-review": 114420,
-    "copilot/gstack-plan-eng-review": 143755,
-    "copilot/gstack-review": 103857,
-    "cursor/gstack-autoplan": 108341,
-    "cursor/gstack-plan-design-review": 107924,
-    "cursor/gstack-plan-devex-review": 113690,
-    "cursor/gstack-plan-eng-review": 142345,
-    "cursor/gstack-review": 122147,
-    "factory/gstack-autoplan": 110619,
-    "factory/gstack-plan-design-review": 111022,
-    "factory/gstack-plan-devex-review": 117053,
-    "factory/gstack-plan-eng-review": 145453,
-    "factory/gstack-review": 125920,
-    "gbrain/gstack-autoplan": 108748,
-    "gbrain/gstack-plan-eng-review": 124972,
-    "gemini/gstack-autoplan": 108899,
-    "gemini/gstack-plan-design-review": 109210,
-    "gemini/gstack-plan-devex-review": 114248,
-    "gemini/gstack-plan-eng-review": 143588,
-    "gemini/gstack-review": 103679,
-    "hermes/gstack-autoplan": 108751,
-    "hermes/gstack-plan-eng-review": 125008,
-    "kiro/gstack-autoplan": 108115,
-    "kiro/gstack-plan-design-review": 107770,
-    "kiro/gstack-plan-devex-review": 113542,
-    "kiro/gstack-plan-eng-review": 142207,
-    "kiro/gstack-review": 121971,
-    "openclaw/gstack-autoplan": 108571,
-    "openclaw/gstack-plan-eng-review": 123487,
-    "opencode/gstack-autoplan": 109090,
-    "opencode/gstack-plan-design-review": 109238,
-    "opencode/gstack-plan-devex-review": 114298,
-    "opencode/gstack-plan-eng-review": 143614,
-    "opencode/gstack-review": 122769,
-    "slate/gstack-autoplan": 108228,
-    "slate/gstack-plan-design-review": 107847,
-    "slate/gstack-plan-devex-review": 113616,
-    "slate/gstack-plan-eng-review": 142276,
-    "slate/gstack-review": 122059
+    "agy/gstack-autoplan": 109657,
+    "agy/gstack-plan-design-review": 109107,
+    "agy/gstack-plan-devex-review": 114949,
+    "agy/gstack-plan-eng-review": 143581,
+    "agy/gstack-review": 104267,
+    "codex/gstack-autoplan": 108400,
+    "codex/gstack-plan-design-review": 110464,
+    "codex/gstack-plan-devex-review": 116457,
+    "codex/gstack-plan-eng-review": 144746,
+    "codex/gstack-review": 103790,
+    "copilot/gstack-autoplan": 109100,
+    "copilot/gstack-plan-design-review": 109373,
+    "copilot/gstack-plan-devex-review": 114411,
+    "copilot/gstack-plan-eng-review": 143746,
+    "copilot/gstack-review": 103848,
+    "cursor/gstack-autoplan": 108332,
+    "cursor/gstack-plan-design-review": 107915,
+    "cursor/gstack-plan-devex-review": 113681,
+    "cursor/gstack-plan-eng-review": 142336,
+    "cursor/gstack-review": 122138,
+    "factory/gstack-autoplan": 110610,
+    "factory/gstack-plan-design-review": 111013,
+    "factory/gstack-plan-devex-review": 117044,
+    "factory/gstack-plan-eng-review": 145444,
+    "factory/gstack-review": 125911,
+    "gbrain/gstack-autoplan": 108739,
+    "gbrain/gstack-plan-eng-review": 124963,
+    "gemini/gstack-autoplan": 108890,
+    "gemini/gstack-plan-design-review": 109201,
+    "gemini/gstack-plan-devex-review": 114239,
+    "gemini/gstack-plan-eng-review": 143579,
+    "gemini/gstack-review": 103670,
+    "hermes/gstack-autoplan": 108742,
+    "hermes/gstack-plan-eng-review": 124999,
+    "kiro/gstack-autoplan": 108106,
+    "kiro/gstack-plan-design-review": 107761,
+    "kiro/gstack-plan-devex-review": 113533,
+    "kiro/gstack-plan-eng-review": 142198,
+    "kiro/gstack-review": 121962,
+    "openclaw/gstack-autoplan": 108562,
+    "openclaw/gstack-plan-eng-review": 123478,
+    "opencode/gstack-autoplan": 109081,
+    "opencode/gstack-plan-design-review": 109229,
+    "opencode/gstack-plan-devex-review": 114289,
+    "opencode/gstack-plan-eng-review": 143605,
+    "opencode/gstack-review": 122760,
+    "slate/gstack-autoplan": 108219,
+    "slate/gstack-plan-design-review": 107838,
+    "slate/gstack-plan-devex-review": 113607,
+    "slate/gstack-plan-eng-review": 142267,
+    "slate/gstack-review": 122050
   }
 }
diff --git a/test/gstack-skill-start.test.ts b/test/gstack-skill-start.test.ts
index 5dca2124f..0c57213d8 100644
--- a/test/gstack-skill-start.test.ts
+++ b/test/gstack-skill-start.test.ts
@@ -118,7 +118,8 @@ describe('gstack-skill-start contract', () => {
     // Worktree-isolated Claude Code sessions refuse a start command named by a
     // variable, a `[ -x ] ||` fallback, or a trailing `|| echo` (reproduced
     // with the pinned CLI). The Claude render is the literal install path;
-    // env-var hosts reach the script through $GSTACK_BIN. A missing helper is
+    // checked-in env-var host renders reach it through $GSTACK_ROOT/bin (an
+    // install-root render names the literal path, GST-882). A missing helper is
     // covered by the degraded-mode prose, not a shell fallback.
     const fence = (text: string) => {
       const at = text.search(/^## Preamble \((?:run first|after scope gate)\)/m);
@@ -130,7 +131,7 @@ describe('gstack-skill-start contract', () => {
     }
     for (const host of ['codex', 'gbrain']) {
       const lines = fence(generatePreamble({ skillName: 'ship', tmplPath: 'ship/SKILL.md.tmpl', host, paths: HOST_PATHS[host], preambleTier: 4 } as TemplateContext)).split('\n');
-      expect(lines.at(-1)).toMatch(/^"\$GSTACK_BIN\/gstack-skill-start" --skill "ship" --model "[^"]+"( --brain-health)?$/);
+      expect(lines.at(-1)).toMatch(/^"\$GSTACK_ROOT\/bin\/gstack-skill-start" --skill "ship" --model "[^"]+"( --brain-health)?$/);
       expect(lines.join('\n')).not.toMatch(/_SS|\$PPID|\|\| echo|\[ -x/);
     }
   });
diff --git a/test/skill-start-plain.test.ts b/test/skill-start-plain.test.ts
index 07f1b56a6..753b2c663 100644
--- a/test/skill-start-plain.test.ts
+++ b/test/skill-start-plain.test.ts
@@ -23,7 +23,7 @@ const ctx = (host: string, installRoot: string | null) =>
 const startFence = (c: TemplateContext) => insertRuntimePreludes(generatePreambleBash(c), c).match(/```bash\n([\s\S]*?)\n```/)![1];
 const GROUPED = /(?:^|[;&|]\s*)\{\s|exit 1;\s*\}/m;
 const sh = (body: string, env: Record<string, string>) =>
-  spawnSync('bash', ['-c', body], { cwd: tmp, encoding: 'utf8', timeout: 10_000, env: { PATH: '/usr/bin:/bin', ...env } });
+  spawnSync('bash', ['-uc', body], { cwd: tmp, encoding: 'utf8', timeout: 10_000, env: { PATH: '/usr/bin:/bin', ...env } });
 function stubStart(root: string) {
   fs.mkdirSync(path.join(root, 'bin'), { recursive: true });
   fs.mkdirSync(path.join(root, 'lib'), { recursive: true });