diff --git a/skills/brainstorm/SKILL.md b/skills/brainstorm/SKILL.md
index c655fa2..7afe571 100644
--- a/skills/brainstorm/SKILL.md
+++ b/skills/brainstorm/SKILL.md
@@ -149,6 +149,48 @@ Inline checklist (not a subagent dispatch):
 
 Fix issues inline. No need to re-review — fix and commit.
 
+### Step 7.5 — Grounding-Check Agent (hard-gate)
+
+Dispatch the read-only `ailang-grounding-check` agent. The agent
+reads the just-written spec with fresh context, extracts its
+load-bearing assumptions about current compiler / checker / codegen
+/ schema behaviour, and for each one searches the workspace for a
+currently-green test that ratifies it.
+
+Dispatch carrier:
+
+| Field | Content |
+|-------|---------|
+| `spec_path` | path to the spec just written in Step 6 |
+| `iteration_scope` | which sections cover the imminent first iteration (verbatim from the brainstorm session) |
+
+The agent returns a `PASS` / `BLOCK` / `INFRA_ERROR` report. Boss
+interpretation:
+
+| Agent status | Boss action |
+|--------------|-------------|
+| `PASS` | Proceed to Step 8. The report goes into the brainstorm chat for the record. |
+| `BLOCK` | Present the report to the user. User either: (a) accepts discard → execute the failure-mode procedure below; or (b) overrides in free chat ("Test `<path>::<name>` ratifies that") → log the override note in the brainstorm chat and proceed to Step 8. |
+| `INFRA_ERROR` | Abort the brainstorm. The spec stays as-is on disk; debug the workspace out-of-band and re-dispatch the agent. |
+
+**Failure-mode procedure (no-override `BLOCK`):**
+
+```bash
+git rm docs/specs/<spec_filename>.md
+# Append a roadmap entry pointing forward to a future re-brainstorm:
+# - [ ] **[<kind>]** <idea title> — <one-line description>
+#   - context: <why this is deferred>
+#   - depends on: <name of the unratified mechanism>
+$EDITOR docs/roadmap.md  # add the entry under the appropriate priority bucket
+git add docs/roadmap.md
+git commit -m "spec: retire <spec topic> — depends on <unratified mechanism>"
+```
+
+After the failure-mode procedure runs, the brainstorm session ENDS.
+There is no Step 8, no Step 9. The idea is parked until the
+dependency ships, at which point a fresh brainstorm session
+re-derives the spec from scratch.
+
 ### Step 8 — Commit + user-review gate
 
 ```bash
@@ -180,7 +222,9 @@ Hand off carries:
 | Direction | Carrier |
 |-----------|---------|
 | user → `brainstorm` | new milestone request |
-| `brainstorm` → `planner` | path to spec + iteration scope |
+| `brainstorm` → `ailang-grounding-check` (Step 7.5) | `spec_path` + `iteration_scope` |
+| `brainstorm` → `planner` (Step 9, on PASS or overridden BLOCK) | path to spec + iteration scope |
+| `brainstorm` → roadmap (Step 7.5, on no-override BLOCK) | `depends on:` entry, spec deleted |
 
 ## Common Rationalisations
 
@@ -210,10 +254,15 @@ Hand off carries:
   criterion" — gate this skill applies during spec writing.
 - **Output target:** `skills/planner/SKILL.md` — only valid next
   skill.
-- **No private agents.** This skill is dialogue-driven. The Boss
-  MAY ad-hoc dispatch `skills/planner/agents/ailang-plan-recon.md`
-  during Step 1 when the milestone enters code territory the Boss
-  has not recently read; this is opt-in and not part of the standard
-  process. Rationale: brainstorm's recon phase is interwoven with
-  the user Q&A — see `docs/specs/2026-05-11-plan-recon-subagent.md`
-  for the full reasoning.
+- **Private agent:** `skills/brainstorm/agents/ailang-grounding-check.md`
+  — dispatched in Step 7.5 as a hard-gate. The agent reads the spec
+  with fresh context and reports PASS / BLOCK / INFRA_ERROR. See
+  `docs/specs/2026-05-11-brainstorm-grounding-check.md` for the
+  design rationale.
+- **Ad-hoc dispatch.** The Boss MAY also ad-hoc dispatch
+  `skills/planner/agents/ailang-plan-recon.md` during Step 1 when
+  the milestone enters code territory the Boss has not recently
+  read; this is opt-in and not part of the standard process.
+  Rationale: brainstorm's recon phase is interwoven with the user
+  Q&A — see `docs/specs/2026-05-11-plan-recon-subagent.md` for the
+  full reasoning.