diff --git a/bin/gstack-community-dashboard b/bin/gstack-community-dashboard
index 2b40b25b7..1a336c96a 100755
--- a/bin/gstack-community-dashboard
+++ b/bin/gstack-community-dashboard
@@ -36,7 +36,7 @@ fi
 # ─── Fetch aggregated stats from edge function ────────────────
 # HTTP status captured (#1947): a backend failure must read as "unknown",
 # never as a healthy "Weekly active installs: 0".
-TMPBODY="$(mktemp)"
+TMPBODY="$(mktemp "${TMPDIR:-/tmp}/gstack-community.XXXXXX")"
 trap 'rm -f "$TMPBODY"' EXIT
 SUPA_HOST="${SUPABASE_URL#*://}"; SUPA_HOST="${SUPA_HOST%%/*}"
 HTTP_CODE="$(_receipted_curl open community-dashboard "$SUPA_HOST" community-pulse-fetch "user-invoked dashboard" --no-payload \
diff --git a/bin/gstack-distill-free-text b/bin/gstack-distill-free-text
index 86cbd8918..0a2fdddec 100755
--- a/bin/gstack-distill-free-text
+++ b/bin/gstack-distill-free-text
@@ -129,7 +129,7 @@ fi
 
 # Heredoc into temp file (avoids $(cat <<'PROMPT'...) which choked the
 # bash parser on apostrophes elsewhere in the script).
-DISTILL_PROMPT_FILE=$(mktemp)
+DISTILL_PROMPT_FILE=$(mktemp "${TMPDIR:-/tmp}/gstack-distill.XXXXXX")
 trap 'rm -f "$DISTILL_PROMPT_FILE"' EXIT
 cat > "$DISTILL_PROMPT_FILE" <<'PROMPT'
 You are gstack dream-cycle distiller. Below are free-text responses the
diff --git a/bin/gstack-jsonl-merge b/bin/gstack-jsonl-merge
index 9c4e22688..ce439d2ac 100755
--- a/bin/gstack-jsonl-merge
+++ b/bin/gstack-jsonl-merge
@@ -45,7 +45,7 @@ BASE="$1"
 OURS="$2"
 THEIRS="$3"
 
-TMP=$(mktemp /tmp/gstack-jsonl-merge.XXXXXX) || exit 1
+TMP=$(mktemp "${TMPDIR:-/tmp}/gstack-jsonl-merge.XXXXXX") || exit 1
 trap 'rm -f "$TMP" 2>/dev/null || true' EXIT
 
 python3 - "$BASE" "$OURS" "$THEIRS" > "$TMP" <<'PYEOF'
diff --git a/bin/gstack-learnings-log b/bin/gstack-learnings-log
index fd0efaa56..4c4a2b6e6 100755
--- a/bin/gstack-learnings-log
+++ b/bin/gstack-learnings-log
@@ -24,7 +24,7 @@ INPUT="$1"
 # Validate and sanitize input. Errors surface (#1950): stderr is captured and
 # printed on failure instead of swallowed — a silent exit 1 here cost Windows
 # users every AI-logged learning.
-TMPERR=$(mktemp)
+TMPERR=$(mktemp "${TMPDIR:-/tmp}/gstack-learnings-log.XXXXXX") || { echo "gstack-learnings-log: could not create a temp file in ${TMPDIR:-/tmp}, so the learning was not recorded. Fix: point TMPDIR at a writable directory." >&2; exit 1; }
 trap 'rm -f "$TMPERR"' EXIT
 set +e
 VALIDATED=$(printf '%s' "$INPUT" | GSTACK_LIB_DIR="$SCRIPT_DIR/../lib" bun -e "
diff --git a/bin/gstack-question-log b/bin/gstack-question-log
index d769bf371..d0d729ca5 100755
--- a/bin/gstack-question-log
+++ b/bin/gstack-question-log
@@ -43,7 +43,7 @@ mkdir -p "$GSTACK_HOME/projects/$SLUG"
 INPUT="$1"
 
 # Validate and enrich from registry.
-TMPERR=$(mktemp)
+TMPERR=$(mktemp "${TMPDIR:-/tmp}/gstack-question-log.XXXXXX") || { echo "gstack-question-log: could not create a temp file in ${TMPDIR:-/tmp}, so the question was not logged. Fix: point TMPDIR at a writable directory." >&2; exit 1; }
 trap 'rm -f "$TMPERR"' EXIT
 set +e
 VALIDATED=$(printf '%s' "$INPUT" | GSTACK_LIB_DIR="$SCRIPT_DIR/../lib" bun -e "
diff --git a/bin/gstack-question-preference b/bin/gstack-question-preference
index 51de1347e..d4452d04e 100755
--- a/bin/gstack-question-preference
+++ b/bin/gstack-question-preference
@@ -143,7 +143,7 @@ do_write() {
   fi
   ensure_file
   local TMPERR
-  TMPERR=$(mktemp)
+  TMPERR=$(mktemp "${TMPDIR:-/tmp}/gstack-question-preference.XXXXXX") || { echo "gstack-question-preference: could not create a temp file in ${TMPDIR:-/tmp}, so the preference was not saved. Fix: point TMPDIR at a writable directory." >&2; return 1; }
   # Use function-local cleanup via RETURN trap so variable lookup only happens
   # while the function is on the stack (avoids EXIT-trap unbound-var race).
   trap "rm -f '$TMPERR'" RETURN
diff --git a/bin/gstack-security-dashboard b/bin/gstack-security-dashboard
index 864fd8f94..5d2d355a0 100755
--- a/bin/gstack-security-dashboard
+++ b/bin/gstack-security-dashboard
@@ -47,7 +47,7 @@ fi
 # Fetch with the HTTP status captured (#1947). A backend failure must read
 # as "unknown", never as a healthy "0 attacks" — fake zeros on a security
 # surface are indistinguishable from good news.
-TMPBODY="$(mktemp)"
+TMPBODY="$(mktemp "${TMPDIR:-/tmp}/gstack-security.XXXXXX")"
 trap 'rm -f "$TMPBODY"' EXIT
 SUPA_HOST="${SUPABASE_URL#*://}"; SUPA_HOST="${SUPA_HOST%%/*}"
 HTTP_CODE="$(_receipted_curl open security-dashboard "$SUPA_HOST" community-pulse-fetch "user-invoked dashboard" --no-payload \
diff --git a/document-release/sections/release-body.md.tmpl b/document-release/sections/release-body.md.tmpl
index 41d257d2a..3e14f84f1 100644
--- a/document-release/sections/release-body.md.tmpl
+++ b/document-release/sections/release-body.md.tmpl
@@ -245,7 +245,7 @@ near the write-back.
 1. Create a private run directory, then replace **every** `<run-dir>` below with its printed absolute path. This literal path survives separate shell calls; do not substitute `$$`.
 
 ```bash
-mktemp -d /tmp/gstack-doc-release-XXXXXXXX
+mktemp -d "${TMPDIR:-/tmp}/gstack-doc-release-XXXXXXXX"
 ```
 
 Fetch the existing PR/MR body using the platform from the shared Step 0. If no PR/MR exists, skip body/title updates and continue to the summary.
diff --git a/ship/sections/pr-body.md.tmpl b/ship/sections/pr-body.md.tmpl
index 259b3fdf4..962587df4 100644
--- a/ship/sections/pr-body.md.tmpl
+++ b/ship/sections/pr-body.md.tmpl
@@ -119,7 +119,7 @@ saved section file path as `DOCS_SECTION_FILE`.
 REDACT_VIS=$(~/.claude/skills/gstack/bin/gstack-config get redact_repo_visibility 2>/dev/null)
 [ -z "$REDACT_VIS" ] && REDACT_VIS=$(gh repo view --json visibility -q .visibility 2>/dev/null | tr 'A-Z' 'a-z')
 REDACT_VIS="${REDACT_VIS:-unknown}"
-PR_BODY_FILE=$(mktemp) || { echo "ERROR: mktemp failed — cannot scan the PR body; refusing to create the PR unscanned." >&2; exit 1; }
+PR_BODY_FILE=$(mktemp "${TMPDIR:-/tmp}/gstack-pr-body.XXXXXX") || { echo "ERROR: mktemp failed — cannot scan the PR body; refusing to create the PR unscanned." >&2; exit 1; }
 { cat <<'PR_BODY_EOF'
 <PR body from above, through the "## Documentation" heading line>
 PR_BODY_EOF
diff --git a/test/document-skills-redaction.test.ts b/test/document-skills-redaction.test.ts
index 4c856e2b3..1d09079b1 100644
--- a/test/document-skills-redaction.test.ts
+++ b/test/document-skills-redaction.test.ts
@@ -35,7 +35,7 @@ describe("/document-release redaction", () => {
     expect(RELEASE).toMatch(/exit 3 \(HIGH\).*do NOT edit/i);
   });
   test("separate shell calls share an explicit run directory and never re-read raw tracker text", () => {
-    expect(RELEASE).toContain('mktemp -d /tmp/gstack-doc-release-XXXXXXXX');
+    expect(RELEASE).toContain('mktemp -d "${TMPDIR:-/tmp}/gstack-doc-release-XXXXXXXX"');
     expect(RELEASE).not.toContain('/tmp/gstack-pr-body-$$');
     expect(RELEASE).not.toContain('<paste the file contents here>');
     expect(RELEASE).toContain('pathlib.Path(sys.argv[1]).read_text()');
diff --git a/test/learnings.test.ts b/test/learnings.test.ts
index e43fe7c04..15f38984f 100644
--- a/test/learnings.test.ts
+++ b/test/learnings.test.ts
@@ -321,3 +321,36 @@ describe('gstack-learnings-search edge cases', () => {
     expect(output).toContain('confidence: 0/10');
   });
 });
+
+// G3 (#2952): the temp file honors TMPDIR, and a temp-file failure says the
+// learning was not recorded instead of exiting with only mktemp's own error.
+describe('G3: learnings-log temp file and TMPDIR', () => {
+  test('logs through a private TMPDIR', () => {
+    const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-learn-tmpdir-'));
+    try {
+      execSync(`${BIN}/gstack-learnings-log '{"skill":"review","type":"pitfall","key":"tmpdir-ok","insight":"x","confidence":5,"source":"observed"}'`, {
+        cwd: ROOT, env: { ...process.env, GSTACK_HOME: tmpDir, TMPDIR: tmp }, encoding: 'utf-8', timeout: 15000,
+      });
+      expect(fs.readFileSync(findLearningsFile()!, 'utf-8')).toContain('tmpdir-ok');
+      expect(fs.readdirSync(tmp)).toEqual([]);
+    } finally {
+      fs.rmSync(tmp, { recursive: true, force: true });
+    }
+  });
+
+  test('an unusable TMPDIR fails loudly and names the dropped learning', () => {
+    let status = 0;
+    let stderr = '';
+    try {
+      execSync(`${BIN}/gstack-learnings-log '{"skill":"review","type":"pitfall","key":"tmpdir-bad","insight":"x","confidence":5,"source":"observed"}'`, {
+        cwd: ROOT, env: { ...process.env, GSTACK_HOME: tmpDir, TMPDIR: path.join(tmpDir, 'does-not-exist') }, encoding: 'utf-8', stdio: 'pipe', timeout: 15000,
+      });
+    } catch (e: any) {
+      status = e.status;
+      stderr = String(e.stderr);
+    }
+    expect(status).not.toBe(0);
+    expect(stderr).toContain('the learning was not recorded');
+    expect(stderr).toContain('TMPDIR');
+  });
+});
diff --git a/test/regression-pr1169-mktemp-fallbacks.test.ts b/test/regression-pr1169-mktemp-fallbacks.test.ts
index 02cfd78f0..4e13403cd 100644
--- a/test/regression-pr1169-mktemp-fallbacks.test.ts
+++ b/test/regression-pr1169-mktemp-fallbacks.test.ts
@@ -75,9 +75,10 @@ describe("#2679: skill-content mktemp guards", () => {
     expect(rendered).toMatch(/REDACT_FILE=\$\(mktemp\)\s*\|\|\s*\{[^}]*exit 1/);
   });
 
-  test("ship pr-body template guards PR_BODY_FILE=$(mktemp) with a loud exit", () => {
+  test("ship pr-body template guards PR_BODY_FILE=$(mktemp ...) with a loud exit", () => {
     const body = readScript("ship/sections/pr-body.md.tmpl");
-    expect(body).toMatch(/PR_BODY_FILE=\$\(mktemp\)\s*\|\|\s*\{[^}]*exit 1/);
+    // G3 (#2952): the mktemp now carries a ${TMPDIR:-/tmp} template.
+    expect(body).toMatch(/PR_BODY_FILE=\$\(mktemp "\$\{TMPDIR:-\/tmp\}\/[^"]+"\)\s*\|\|\s*\{[^}]*exit 1/);
   });
 
   test("ship pr-body GitLab path sends the SCANNED file, never a re-rendered heredoc", () => {
@@ -151,3 +152,32 @@ describe("PR #1169 bug #5: supabase/verify-rls.sh mktemp fallback", () => {
     expect(guard).not.toBeNull();
   });
 });
+
+// G3 (#2952): bare `mktemp`, `mktemp -t` and literal `/tmp/` templates ignore
+// the TMPDIR a sandboxed agent shell sets, and a failed mktemp under `set -e`
+// silently dropped the learning or question being logged.
+describe("G3: mktemp honors TMPDIR in logging bins and lane-owned skill bash", () => {
+  const FILES = [
+    "bin/gstack-learnings-log",
+    "bin/gstack-question-log",
+    "bin/gstack-question-preference",
+    "bin/gstack-jsonl-merge",
+    "bin/gstack-distill-free-text",
+    "bin/gstack-community-dashboard",
+    "bin/gstack-security-dashboard",
+    "ship/sections/pr-body.md.tmpl",
+    "document-release/sections/release-body.md.tmpl",
+  ];
+  for (const rel of FILES) {
+    test(`${rel}: every temp-dir mktemp uses a \${TMPDIR:-/tmp} template`, () => {
+      const calls = [...readScript(rel).matchAll(/(?:\$\(|^[ \t]*)(mktemp\b[^\n)]*)/gm)].map((m) => m[1]);
+      expect(calls.length).toBeGreaterThan(0);
+      for (const call of calls) {
+        expect(call).not.toMatch(/^mktemp\s*$/);
+        expect(call).not.toMatch(/^mktemp\s+(-d\s+)?-t\b/);
+        expect(call).not.toMatch(/^mktemp\s+(-d\s+)?["']?\/tmp\//);
+        expect(call).toMatch(/\$\{TMPDIR:-\/tmp\}\//);
+      }
+    });
+  }
+});
diff --git a/test/ship-publication-gates.test.ts b/test/ship-publication-gates.test.ts
index e305ec529..19cf71955 100644
--- a/test/ship-publication-gates.test.ts
+++ b/test/ship-publication-gates.test.ts
@@ -52,7 +52,7 @@ exec ${JSON.stringify(process.execPath)} ${JSON.stringify(scanner)} "$@"
 
 test('publication composes the saved documentation section unchanged and refuses to scan without it', () => {
   const block = template.match(/```bash\n(: "\$\{NEW_TITLE:[\s\S]*?)\n```/)?.[1]!;
-  const compose = block.slice(block.indexOf('PR_BODY_FILE=$(mktemp)'), block.indexOf('~/.claude/skills/gstack/bin/gstack-redact --from-file'));
+  const compose = block.slice(block.indexOf('PR_BODY_FILE=$(mktemp'), block.indexOf('~/.claude/skills/gstack/bin/gstack-redact --from-file'));
   const root = mkdtempSync(join(tmpdir(), 'ship-compose-'));
   try {
     const section = '**Status:** current — no edits.\n\n- Diagram drift: none (no diagrams in any doc).';
diff --git a/test/workflow-excerpt.test.ts b/test/workflow-excerpt.test.ts
index 9744e52df..4b82715e4 100644
--- a/test/workflow-excerpt.test.ts
+++ b/test/workflow-excerpt.test.ts
@@ -108,7 +108,7 @@ describe('workflow judge excerpts', () => {
   test('ship publishes existing PRs only after shared body composition and scan', () => {
     const text = readWorkflowExcerpt('ship/SKILL.md', '# Ship:', '## Important Rules');
     const publish = text.slice(text.indexOf('## Step 19:'), text.indexOf('## Step 20:'));
-    const compose = publish.indexOf('PR_BODY_FILE=$(mktemp)');
+    const compose = publish.indexOf('PR_BODY_FILE=$(mktemp');
     const scan = publish.indexOf('gstack-redact --from-file "$PR_BODY_FILE"');
     const edit = publish.indexOf('gh pr edit --body-file');
     expect(compose).toBeGreaterThan(0);