diff --git a/src/runtime/inject-context.ts b/src/runtime/inject-context.ts
index f78d0d6..4709579 100644
--- a/src/runtime/inject-context.ts
+++ b/src/runtime/inject-context.ts
@@ -22,6 +22,23 @@ export function claudeMdKey(prompt: string, ctx: string): string {
   return `claude-md:${hashText(prompt)}:${hashText(ctx)}`;
 }
 
+/**
+ * Extract the APEX preamble portion of a `buildClaudeMdContext` result, i.e.
+ * everything BEFORE the `# <docName>\n` root-doc block it prepends on dev
+ * prompts. Returns "" when `ctx` has no preamble (plain prompt: `ctx` starts
+ * directly with the root-doc heading).
+ * @param ctx - The full `buildClaudeMdContext` return value.
+ * @param docName - Root doc file name (e.g. "AGENTS.md").
+ * @returns The preamble text, or "" when absent.
+ */
+function extractApexPreamble(ctx: string, docName: string): string {
+  const heading = `# ${docName}\n`;
+  if (ctx.startsWith(heading)) return "";
+  const sep = `\n\n${heading}`;
+  const idx = ctx.indexOf(sep);
+  return idx === -1 ? "" : ctx.slice(0, idx);
+}
+
 /**
  * UserPromptSubmit context injection: render the CLAUDE.md (+ optional APEX)
  * preamble as a Claude `additionalContext` response, or "" when nothing to emit.
@@ -29,6 +46,13 @@ export function claudeMdKey(prompt: string, ctx: string): string {
  * near-simultaneous double-fire of the SAME turn (identical prompt AND identical
  * block, within {@link DEDUP_WINDOW_MS}) is suppressed. The invariant "CLAUDE.md
  * is emitted on EVERY message" is thus preserved.
+ *
+ * On kimi specifically, the root doc body is dropped from the emitted text:
+ * Kimi loads `<kimiHome>/AGENTS.md` natively at session start (`apex-target.ts`),
+ * so re-injecting its full body on every prompt is redundant terminal noise
+ * (kimi has no model-only hook channel — `runtime/inform.ts`). The APEX
+ * preamble, which is NOT part of `AGENTS.md`, is still emitted in full when the
+ * prompt is dev-shaped; a plain prompt leaves only the notice.
  * @param prompt - The raw user prompt.
  * @param cwd - Project root (for project-type detection).
  * @param id - Harness target id (defaults to "claude-code" — zero-regression default).
@@ -38,7 +62,12 @@ export function promptSubmitContext(prompt: string, cwd: string, id: string = "c
   const ctx = buildClaudeMdContext(prompt, cwd, id);
   if (!ctx) return "";
   if (!oncePerWindow(claudeMdKey(prompt, ctx), DEDUP_WINDOW_MS)) return "";
-  return renderInform(id, "UserPromptSubmit", ctx, `${apexDocName(id)} injected`);
+  const notice = `${apexDocName(id)} injected`;
+  if (id === "kimi") {
+    const preamble = extractApexPreamble(ctx, apexDocName(id));
+    return preamble ? renderInform(id, "UserPromptSubmit", preamble, notice) : notice;
+  }
+  return renderInform(id, "UserPromptSubmit", ctx, notice);
 }
 
 /**
diff --git a/src/runtime/lifecycle/inject-rules.ts b/src/runtime/lifecycle/inject-rules.ts
index da6af27..9f3d882 100644
--- a/src/runtime/lifecycle/inject-rules.ts
+++ b/src/runtime/lifecycle/inject-rules.ts
@@ -1,6 +1,7 @@
 import { existsSync, readdirSync, readFileSync } from "node:fs";
 import { join } from "node:path";
 import { renderInform } from "../inform";
+import { rulesInAgentsMd } from "./kimi-rules-native";
 
 /** Read & concatenate all `*.md` files (sorted) under `rulesDir`. */
 export function readRules(rulesDir: string): string {
@@ -29,6 +30,13 @@ export function readRules(rulesDir: string): string {
  * with the *actual* `hookEventName` — the spec requires it to match the firing
  * event (a hardcoded "SessionStart" is non-conforming and may be dropped on
  * UserPromptSubmit/SubagentStart).
+ *
+ * On kimi's `UserPromptSubmit` specifically, when the corpus is already fenced
+ * inside `<kimiHome>/AGENTS.md` (native load, {@link rulesInAgentsMd}), only the
+ * notice is emitted — the re-injected corpus would otherwise dump into the
+ * user's terminal on every single prompt for no model-context benefit.
+ * `SessionStart`/`SubagentStart` always keep the full corpus (session bootstrap
+ * / sub-agent contexts need it regardless of the native AGENTS.md load).
  * @param pluginRoot - `CLAUDE_PLUGIN_ROOT` of the claude-rules plugin.
  * @param event - The firing hook event name (e.g. "SessionStart").
  * @param id - Harness target id (defaults to "claude-code" — zero-regression default).
@@ -36,5 +44,7 @@ export function readRules(rulesDir: string): string {
  */
 export function injectRules(pluginRoot: string, event: string, id: string = "claude-code"): string {
   const content = readRules(join(pluginRoot, "rules"));
-  return content ? renderInform(id, event, content, "rules 00-08 injected") : "";
+  if (!content) return "";
+  if (id === "kimi" && event === "UserPromptSubmit" && rulesInAgentsMd()) return "rules 00-08 injected";
+  return renderInform(id, event, content, "rules 00-08 injected");
 }
diff --git a/src/runtime/lifecycle/kimi-rules-native.ts b/src/runtime/lifecycle/kimi-rules-native.ts
new file mode 100644
index 0000000..7844717
--- /dev/null
+++ b/src/runtime/lifecycle/kimi-rules-native.ts
@@ -0,0 +1,44 @@
+/**
+ * Guard for the kimi notice-only rules injection. Kimi Code CLI has no
+ * model-only hook channel (`src/runtime/inform.ts`) — every `UserPromptSubmit`
+ * stdout is BOTH appended to the model's context AND rendered raw in the
+ * user's terminal. `injectRules` (`inject-rules.ts`) normally re-injects the
+ * full ~18 Ko rules corpus on every prompt; when the installer has already
+ * merged that same corpus into `<kimiHome>/AGENTS.md` — which Kimi loads
+ * natively at session start via its documented `${agents_md}` mechanism,
+ * independent of hooks — the re-injection is pure noise the user has to
+ * scroll past. Confirmed present, fenced, in the local install:
+ * `~/.kimi-code/AGENTS.md:87` / `:335`.
+ *
+ * Fail-safe semantics: fences absent, file absent, or any read error ⟹
+ * `false` — the caller then falls back to the full corpus. A dump is
+ * verbose but never wrong; a false `true` would silently drop the rules.
+ */
+import { existsSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+import { harnessHome } from "../../config/home-dir";
+
+/** Opening fence the fusengine installer writes around the merged corpus. */
+const FENCE_START = "<!-- fusengine:kimi-rules:start -->";
+
+/** Closing fence the fusengine installer writes around the merged corpus. */
+const FENCE_END = "<!-- fusengine:kimi-rules:end -->";
+
+/**
+ * Check whether the kimi rules corpus is already present, fenced, inside
+ * `<kimiHome>/AGENTS.md`.
+ * @param home - Kimi home dir override (defaults to `harnessHome("kimi")`,
+ * which honors `KIMI_CODE_HOME`).
+ * @returns `true` only when both fences are found in a readable file.
+ */
+export function rulesInAgentsMd(home?: string): boolean {
+  try {
+    const kimiHome = home ?? harnessHome("kimi");
+    const agentsMd = join(kimiHome, "AGENTS.md");
+    if (!existsSync(agentsMd)) return false;
+    const content = readFileSync(agentsMd, "utf-8");
+    return content.includes(FENCE_START) && content.includes(FENCE_END);
+  } catch {
+    return false;
+  }
+}
diff --git a/test/fixtures/inform-matrix.golden.json b/test/fixtures/inform-matrix.golden.json
new file mode 100644
index 0000000..82d3bda
--- /dev/null
+++ b/test/fixtures/inform-matrix.golden.json
@@ -0,0 +1,34 @@
+{
+  "injectRules|claude-code|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|claude-code|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|claude-code|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|codex|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|codex|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|codex|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|gemini-cli|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|gemini-cli|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|gemini-cli|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# 00 alpha\\nalpha body\\n\\n\\n# 01 beta\\nbeta body\\n\"},\"systemMessage\":\"rules 00-08 injected\"}",
+  "injectRules|kimi|SessionStart|-": "# 00 alpha\nalpha body\n\n\n# 01 beta\nbeta body\n\n\nrules 00-08 injected",
+  "injectRules|kimi|SubagentStart|-": "# 00 alpha\nalpha body\n\n\n# 01 beta\nbeta body\n\n\nrules 00-08 injected",
+  "injectRules|kimi|UserPromptSubmit|-": "# 00 alpha\nalpha body\n\n\n# 01 beta\nbeta body\n\n\nrules 00-08 injected",
+  "lessons|claude-code|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|claude-code|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|claude-code|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|codex|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|codex|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|codex|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|gemini-cli|SessionStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SessionStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|gemini-cli|SubagentStart|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"SubagentStart\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|gemini-cli|UserPromptSubmit|-": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"Project lessons — never reproduce these:\\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\"},\"systemMessage\":\"lessons injected\"}",
+  "lessons|kimi|SessionStart|-": "Project lessons — never reproduce these:\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\n\nlessons injected",
+  "lessons|kimi|SubagentStart|-": "Project lessons — never reproduce these:\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\n\nlessons injected",
+  "lessons|kimi|UserPromptSubmit|-": "Project lessons — never reproduce these:\n- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\nYou may append OR refine/merge/dedupe bullets in MEMORY/LESSON.md — keep it terse.\n\nlessons injected",
+  "promptSubmit|claude-code|UserPromptSubmit|dev": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"INSTRUCTION: This is a development task. Use APEX methodology:\\n\\n**TRACKING FILE**: [project]/.claude/apex/task.json — create it yourself via apex-methodology Step 0 (init-tracking) if missing\\n\\n1. **ANALYZE** (MANDATORY - 3 AGENTS IN PARALLEL):\\n   - explore-codebase + research-expert + general-purpose (framework expertise)\\n   - Project type detected: generic\\n\\n2. **PLAN**: Use TaskCreate to break down tasks (<100 lines per file)\\n\\n3. **EXECUTE**: general-purpose, follow SOLID principles, split at 90 lines\\n\\n4. **eLICIT**: self-review with NAMED elicitation techniques (apex ref 03.5-elicit) — fix findings BEFORE validation\\n\\n5. **VERIFY**: functional check — run it, confirm references⇔declarations consistency\\n\\n6. **eXAMINE**: Run sniper agent after ANY modification\\n\\n**GATE**: eLicit + Verify BEFORE sniper — NEVER skip.\\n\\n**IMPORTANT**: Read .claude/apex/task.json to check documentation status before writing code.\\n\\n# CLAUDE.md\\n# fixture CLAUDE.md for .claude\\nBODY .claude\\n\"},\"systemMessage\":\"CLAUDE.md injected\"}",
+  "promptSubmit|claude-code|UserPromptSubmit|plain": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# CLAUDE.md\\n# fixture CLAUDE.md for .claude\\nBODY .claude\\n\"},\"systemMessage\":\"CLAUDE.md injected\"}",
+  "promptSubmit|codex|UserPromptSubmit|dev": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"INSTRUCTION: This is a development task. Use APEX methodology:\\n\\n**TRACKING FILE**: [project]/.codex/apex/task.json — create it yourself via apex-methodology Step 0 (init-tracking) if missing\\n\\n1. **ANALYZE** (MANDATORY - 3 AGENTS IN PARALLEL):\\n   - explore-codebase + research-expert + general-purpose (framework expertise)\\n   - Project type detected: generic\\n\\n2. **PLAN**: Use update_plan to break down tasks (<100 lines per file)\\n\\n3. **EXECUTE**: general-purpose, follow SOLID principles, split at 90 lines\\n\\n4. **eLICIT**: self-review with NAMED elicitation techniques (apex ref 03.5-elicit) — fix findings BEFORE validation\\n\\n5. **VERIFY**: functional check — run it, confirm references⇔declarations consistency\\n\\n6. **eXAMINE**: Run sniper agent after ANY modification\\n\\n**GATE**: eLicit + Verify BEFORE sniper — NEVER skip.\\n\\n**IMPORTANT**: Read .codex/apex/task.json to check documentation status before writing code.\\n\\n# AGENTS.md\\n# fixture AGENTS.md for .codex\\nBODY .codex\\n\"},\"systemMessage\":\"AGENTS.md injected\"}",
+  "promptSubmit|codex|UserPromptSubmit|plain": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# AGENTS.md\\n# fixture AGENTS.md for .codex\\nBODY .codex\\n\"},\"systemMessage\":\"AGENTS.md injected\"}",
+  "promptSubmit|gemini-cli|UserPromptSubmit|dev": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"INSTRUCTION: This is a development task. Use APEX methodology:\\n\\n**TRACKING FILE**: [project]/.gemini/apex/task.json — create it yourself via apex-methodology Step 0 (init-tracking) if missing\\n\\n1. **ANALYZE** (MANDATORY - 3 AGENTS IN PARALLEL):\\n   - explore-codebase + research-expert + general-purpose (framework expertise)\\n   - Project type detected: generic\\n\\n2. **PLAN**: Use TaskCreate to break down tasks (<100 lines per file)\\n\\n3. **EXECUTE**: general-purpose, follow SOLID principles, split at 90 lines\\n\\n4. **eLICIT**: self-review with NAMED elicitation techniques (apex ref 03.5-elicit) — fix findings BEFORE validation\\n\\n5. **VERIFY**: functional check — run it, confirm references⇔declarations consistency\\n\\n6. **eXAMINE**: Run sniper agent after ANY modification\\n\\n**GATE**: eLicit + Verify BEFORE sniper — NEVER skip.\\n\\n**IMPORTANT**: Read .gemini/apex/task.json to check documentation status before writing code.\\n\\n# CLAUDE.md\\n# fixture CLAUDE.md for .gemini\\nBODY .gemini\\n\"},\"systemMessage\":\"CLAUDE.md injected\"}",
+  "promptSubmit|gemini-cli|UserPromptSubmit|plain": "{\"hookSpecificOutput\":{\"hookEventName\":\"UserPromptSubmit\",\"additionalContext\":\"# CLAUDE.md\\n# fixture CLAUDE.md for .gemini\\nBODY .gemini\\n\"},\"systemMessage\":\"CLAUDE.md injected\"}",
+  "promptSubmit|kimi|UserPromptSubmit|dev": "INSTRUCTION: This is a development task. Use APEX methodology:\n\n**TRACKING FILE**: [project]/.kimi-code/apex/task.json — create it yourself via apex-methodology Step 0 (init-tracking) if missing\n\n1. **ANALYZE** (MANDATORY - 3 AGENTS IN PARALLEL):\n   - explore-codebase + research-expert + general-purpose (framework expertise)\n   - Project type detected: generic\n\n2. **PLAN**: Use TodoList to break down tasks (<100 lines per file)\n\n3. **EXECUTE**: general-purpose, follow SOLID principles, split at 90 lines\n\n4. **eLICIT**: self-review with NAMED elicitation techniques (apex ref 03.5-elicit) — fix findings BEFORE validation\n\n5. **VERIFY**: functional check — run it, confirm references⇔declarations consistency\n\n6. **eXAMINE**: Run sniper agent after ANY modification\n\n**GATE**: eLicit + Verify BEFORE sniper — NEVER skip.\n\n**IMPORTANT**: Read .kimi-code/apex/task.json to check documentation status before writing code.\n\nAGENTS.md injected",
+  "promptSubmit|kimi|UserPromptSubmit|plain": "AGENTS.md injected"
+}
diff --git a/test/helpers/capture-inform-golden.ts b/test/helpers/capture-inform-golden.ts
new file mode 100644
index 0000000..2bfb17e
--- /dev/null
+++ b/test/helpers/capture-inform-golden.ts
@@ -0,0 +1,23 @@
+/**
+ * @module test/helpers/capture-inform-golden
+ * Manual, one-shot script: run `bun run test/helpers/capture-inform-golden.ts`
+ * to (re)write `test/fixtures/inform-matrix.golden.json` from the current
+ * `src/` behavior.
+ *
+ * NEVER re-run this in the same commit as a behavior change to `renderInform`
+ * (or anything it calls transitively). The golden is the WITNESS that the
+ * pre-change code respected the zero-regression theorem's hypotheses — it
+ * must be captured and committed BEFORE the change, as its own commit.
+ * Regenerating it alongside the change makes the proof and the change
+ * indistinguishable on review: a diff that "updates the golden" could just as
+ * easily be hiding a real regression as reflecting an intentional new branch.
+ */
+import { mkdirSync, writeFileSync } from "node:fs";
+import { join } from "node:path";
+import { runMatrix } from "./inform-matrix-run";
+
+const outDir = join(import.meta.dir, "..", "fixtures");
+const outFile = join(outDir, "inform-matrix.golden.json");
+mkdirSync(outDir, { recursive: true });
+writeFileSync(outFile, `${JSON.stringify(runMatrix(), null, 2)}\n`);
+console.log(`wrote ${outFile}`);
diff --git a/test/helpers/capture-run.ts b/test/helpers/capture-run.ts
new file mode 100644
index 0000000..98b0776
--- /dev/null
+++ b/test/helpers/capture-run.ts
@@ -0,0 +1,19 @@
+/**
+ * @module test/helpers/capture-run
+ * Entry point of the CAPTURE CHILD PROCESS. Runs isolated from the parent
+ * because Bun snapshots `$HOME` at process start — mutating
+ * `process.env.HOME` in the parent process would NOT change what
+ * `os.homedir()` returns there (measured on Bun 1.3.14). Spawning a fresh
+ * process with `HOME` set in its own env is the only way to pin it.
+ * Reads the fixture root from `MATRIX_ROOT` (never `process.argv`, since the
+ * parent passes it via the child's env allowlist — see `childEnv`).
+ */
+import { pathsFor } from "./inform-matrix-env";
+import { captureMatrix } from "./inform-matrix";
+
+const root = process.env.MATRIX_ROOT;
+if (!root) {
+  console.error("capture-run: MATRIX_ROOT env var is required");
+  process.exit(2);
+}
+process.stdout.write(JSON.stringify(captureMatrix(pathsFor(root))));
diff --git a/test/helpers/inform-matrix-env.ts b/test/helpers/inform-matrix-env.ts
new file mode 100644
index 0000000..f70f03e
--- /dev/null
+++ b/test/helpers/inform-matrix-env.ts
@@ -0,0 +1,110 @@
+/**
+ * @module test/helpers/inform-matrix-env
+ * Hermetic fixture tree for the zero-regression golden capture.
+ *
+ * The emitters under capture read AMBIENT state: `$HOME` (root instructions doc,
+ * the marketplace scan, the dedup sidecar), the project dir (`MEMORY/LESSON.md`,
+ * project-type detection), `process.env` (harness detection, SOLID ceiling), and
+ * a clock. Left ambient, the golden would encode THIS machine on THIS day and
+ * prove nothing. This module builds the fixtures; the capture itself runs in a
+ * CHILD process (see `inform-matrix-run`) because Bun snapshots `$HOME` at
+ * process start — `os.homedir()` ignores a later `process.env.HOME` mutation
+ * (measured on Bun 1.3.14), so in-process pinning silently reads the real home.
+ */
+import { mkdirSync, mkdtempSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+/** Pinned clock for every emitter that takes one (lessons curation). */
+export const NOW = 1_700_000_000_000;
+
+/**
+ * Home segment → root instructions doc, mirroring `harnessHomeSegment` /
+ * `apexDocName`. Bodies differ per segment on purpose: `claude-code` and
+ * `gemini-cli` both read `CLAUDE.md`, and identical bodies would collide on the
+ * `oncePerWindow` content hash — blanking one cell of the golden in silence.
+ */
+const HARNESS_DOCS: ReadonlyArray<readonly [string, string]> = [
+  [".claude", "CLAUDE.md"],
+  [".codex", "AGENTS.md"],
+  [".gemini", "CLAUDE.md"],
+  [".kimi-code", "AGENTS.md"],
+];
+
+/** Fixture lesson: one dated bullet, stable under curation at {@link NOW}. */
+const LESSON = "- [2026-01-01 10:00] Fixture lesson body. → Fixture rule. [TRIGGERS keyword:fixture]\n";
+
+/**
+ * `package.json` marker. NOT cosmetic: `projectRoot()` walks up for `.git` then
+ * `package.json` and falls back to `process.cwd()` — without this marker the
+ * lessons emitter would read AND REWRITE this repo's own `MEMORY/LESSON.md`.
+ * Its content must match no framework probe, so detection stays "generic".
+ */
+const PKG = '{"name":"golden-fixture","version":"0.0.0"}\n';
+
+/** Absolute paths of one fixture tree, shared by the parent and the capture child. */
+export interface MatrixPaths {
+  /** Temp root holding `home/`, `plugin/` and the project dirs. */
+  root: string;
+  /** `$HOME` of the capture child. */
+  home: string;
+  /** Plugin root passed to `injectRules` (holds `rules/*.md`). */
+  pluginRoot: string;
+  /** Stable project dir, for the emitters that only READ it. */
+  project: string;
+}
+
+/** Derive every fixture path from the root, so parent and child never disagree. */
+export function pathsFor(root: string): MatrixPaths {
+  return {
+    root,
+    home: join(root, "home"),
+    pluginRoot: join(root, "plugin"),
+    project: join(root, "project-stable"),
+  };
+}
+
+/**
+ * Create a project dir carrying the markers `projectRoot` + detection need.
+ * Lessons curation REWRITES `LESSON.md`, so each lessons cell gets its OWN dir —
+ * a shared one would make cell N depend on cell N-1.
+ * @param root - Fixture root.
+ * @param tag - Unique suffix for this project dir.
+ * @returns The created project dir.
+ */
+export function makeProject(root: string, tag: string): string {
+  const dir = join(root, `project-${tag}`);
+  mkdirSync(join(dir, "MEMORY"), { recursive: true });
+  writeFileSync(join(dir, "package.json"), PKG);
+  writeFileSync(join(dir, "MEMORY", "LESSON.md"), LESSON);
+  return dir;
+}
+
+/**
+ * Build the fixture tree under a fresh temp root.
+ * @returns The fixture paths.
+ */
+export function buildFixtures(): MatrixPaths {
+  const paths = pathsFor(mkdtempSync(join(tmpdir(), "inform-golden-")));
+  for (const [seg, doc] of HARNESS_DOCS) {
+    mkdirSync(join(paths.home, seg), { recursive: true });
+    writeFileSync(join(paths.home, seg, doc), `# fixture ${doc} for ${seg}\nBODY ${seg}\n`);
+  }
+  mkdirSync(join(paths.pluginRoot, "rules"), { recursive: true });
+  writeFileSync(join(paths.pluginRoot, "rules", "00-alpha.md"), "# 00 alpha\nalpha body\n");
+  writeFileSync(join(paths.pluginRoot, "rules", "01-beta.md"), "# 01 beta\nbeta body\n");
+  makeProject(paths.root, "stable");
+  return paths;
+}
+
+/**
+ * Environment of the capture child — an ALLOWLIST, never an inherit. Inheriting
+ * would leak `CLAUDECODE` (or any of the 15 other harness markers), making
+ * `detectHarness()` answer "claude-code" here and "unknown" in CI, plus every
+ * ambient `FUSE_*` that moves the SOLID ceiling.
+ * @param paths - The fixture tree.
+ * @returns The exact env handed to the child.
+ */
+export function childEnv(paths: MatrixPaths): Record<string, string> {
+  return { PATH: process.env.PATH ?? "", HOME: paths.home, MATRIX_ROOT: paths.root };
+}
diff --git a/test/helpers/inform-matrix-run.ts b/test/helpers/inform-matrix-run.ts
new file mode 100644
index 0000000..f4fb0ed
--- /dev/null
+++ b/test/helpers/inform-matrix-run.ts
@@ -0,0 +1,33 @@
+/**
+ * @module test/helpers/inform-matrix-run
+ * Parent-side driver: builds the fixtures, spawns the capture child
+ * (`capture-run.ts`) with an allowlisted env, parses its stdout, validates
+ * portability, and cleans up. Never mutates the PARENT process's own
+ * `process.env` — `bun test` runs every file sequentially in one shared
+ * process, so a parent-side mutation would leak into the other ~180 test
+ * files in the suite.
+ */
+import { spawnSync } from "node:child_process";
+import { rmSync } from "node:fs";
+import { join } from "node:path";
+import { buildFixtures, childEnv } from "./inform-matrix-env";
+import { assertPortable } from "./inform-matrix";
+
+/**
+ * Run the full capture in an isolated child process and return the golden.
+ * @returns The 32-cell golden map.
+ */
+export function runMatrix(): Record<string, string> {
+  const paths = buildFixtures();
+  const r = spawnSync("bun", ["run", join(import.meta.dir, "capture-run.ts")], {
+    env: childEnv(paths),
+    encoding: "utf8",
+  });
+  if (r.status !== 0) {
+    throw new Error(`capture-run.ts exited ${String(r.status)}: ${r.stderr}`);
+  }
+  const cells = JSON.parse(r.stdout) as Record<string, string>;
+  assertPortable(cells, paths.root);
+  rmSync(paths.root, { recursive: true, force: true });
+  return cells;
+}
diff --git a/test/helpers/inform-matrix.ts b/test/helpers/inform-matrix.ts
new file mode 100644
index 0000000..698fca3
--- /dev/null
+++ b/test/helpers/inform-matrix.ts
@@ -0,0 +1,70 @@
+/**
+ * @module test/helpers/inform-matrix
+ * Builds the full 32-cell golden matrix: (id × event × emitter) triples,
+ * captured DETERMINISTICALLY inside the hermetic fixture tree from
+ * `inform-matrix-env`. Runs inside the capture child (see `capture-run`) so
+ * every ambient read resolves against the fixtures, never the real machine.
+ */
+import { injectRules } from "../../src/runtime/lifecycle/inject-rules";
+import { promptSubmitContext } from "../../src/runtime/inject-context";
+import { dispatchLessons } from "../../src/runtime/lifecycle/lessons/dispatch";
+import { NOW, makeProject } from "./inform-matrix-env";
+import type { MatrixPaths } from "./inform-matrix-env";
+
+/** Harness targets covered by the matrix. */
+export const IDS = ["claude-code", "codex", "gemini-cli", "kimi"] as const;
+
+/** Hook events covered by the matrix. */
+export const EVENTS = ["SessionStart", "UserPromptSubmit", "SubagentStart"] as const;
+
+/**
+ * Prompts for `promptSubmitContext`: "dev" matches both `DEV_VERBS`
+ * (`src/policy/claude-md-context.ts`) and `DEV_KEYWORDS`
+ * (`src/policy/detect-project.ts`), so it exercises the APEX preamble path.
+ * "plain" matches NEITHER regex (verified against both patterns before
+ * writing this fixture) — it exercises the plain CLAUDE.md-only path.
+ */
+const PROMPTS = [
+  ["dev", "implement the parser"],
+  ["plain", "quelle heure est-il"],
+] as const;
+
+/**
+ * Capture every (id × event) cell for the three emitters under test, plus the
+ * two prompt-kind variants of `promptSubmitContext`. Iteration is purely
+ * synchronous — order comes from the loop structure, never from scheduling —
+ * and the final map is key-sorted so the golden JSON is diffable line by line
+ * regardless of iteration order.
+ * @param paths - The hermetic fixture tree (see {@link buildFixtures}).
+ * @returns The 32-cell golden map, keyed `emitter|id|event|extra`.
+ */
+export function captureMatrix(paths: MatrixPaths): Record<string, string> {
+  const cells: Array<[string, string]> = [];
+  for (const id of IDS) {
+    for (const event of EVENTS) {
+      cells.push([`injectRules|${id}|${event}|-`, injectRules(paths.pluginRoot, event, id)]);
+      const lessonsDir = makeProject(paths.root, `${id}-${event}`);
+      cells.push([`lessons|${id}|${event}|-`, dispatchLessons(event, {}, lessonsDir, NOW, id)]);
+      if (event === "UserPromptSubmit") {
+        for (const [kind, prompt] of PROMPTS) {
+          cells.push([`promptSubmit|${id}|UserPromptSubmit|${kind}`, promptSubmitContext(prompt, paths.project, id)]);
+        }
+      }
+    }
+  }
+  cells.sort(([a], [b]) => (a < b ? -1 : a > b ? 1 : 0));
+  return Object.fromEntries(cells);
+}
+
+/**
+ * Guard against a non-portable golden: a captured value that embeds the
+ * fixture's own temp root would tie the golden to this run's random path and
+ * break on every future capture.
+ * @param cells - The captured golden map.
+ * @param root - The fixture root whose path must never leak into a value.
+ */
+export function assertPortable(cells: Record<string, string>, root: string): void {
+  for (const [key, value] of Object.entries(cells)) {
+    if (value.includes(root)) throw new Error(`non-portable golden cell "${key}" embeds fixture root ${root}`);
+  }
+}
diff --git a/test/inform-matrix.characterization.test.ts b/test/inform-matrix.characterization.test.ts
new file mode 100644
index 0000000..ed00d8e
--- /dev/null
+++ b/test/inform-matrix.characterization.test.ts
@@ -0,0 +1,25 @@
+/**
+ * @module test/inform-matrix.characterization
+ * Zero-regression golden for `renderInform` and its three call sites
+ * (`injectRules`, `dispatchLessons`, `promptSubmitContext`) across every
+ * (harness id × hook event) combination.
+ *
+ * A diff on ANY cell other than `kimi × UserPromptSubmit` IS the regression:
+ * the theorem this golden witnesses is `f'(x) = g(x) if P(x), f(x) otherwise`
+ * ⟹ `∀x. ¬P(x) ⟹ f'(x) = f(x)` — every non-kimi/non-UserPromptSubmit cell is
+ * an `x` where `¬P(x)` holds, so it MUST stay byte-identical. The golden is
+ * never updated to make new code pass; see `capture-inform-golden.ts` for why.
+ */
+import { describe, expect, test } from "bun:test";
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+import { runMatrix } from "./helpers/inform-matrix-run";
+
+const goldenPath = join(import.meta.dir, "fixtures", "inform-matrix.golden.json");
+
+describe("renderInform zero-regression matrix", () => {
+  test("every (id x event x emitter) cell matches the captured golden", () => {
+    const golden = JSON.parse(readFileSync(goldenPath, "utf8")) as Record<string, string>;
+    expect(runMatrix()).toEqual(golden);
+  });
+});
diff --git a/test/kimi-notice-only.test.ts b/test/kimi-notice-only.test.ts
new file mode 100644
index 0000000..aee4802
--- /dev/null
+++ b/test/kimi-notice-only.test.ts
@@ -0,0 +1,92 @@
+/**
+ * @module test/kimi-notice-only
+ * Dedicated unit tests for the kimi notice-only injection (theorem
+ * `f'(x) = g(x) if P(x), f(x) otherwise`, `P(x) ≡ id="kimi" ∧
+ * event="UserPromptSubmit"`). The golden matrix
+ * (`inform-matrix.characterization.test.ts`) proves the fail-safe default
+ * (fences absent in its fixture); these tests exercise the fenced-present
+ * branch directly, plus the SessionStart/SubagentStart/claude-code
+ * non-regression cases.
+ */
+import { afterAll, afterEach, describe, expect, test } from "bun:test";
+import { mkdirSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { rulesInAgentsMd } from "../src/runtime/lifecycle/kimi-rules-native";
+import { injectRules } from "../src/runtime/lifecycle/inject-rules";
+
+const FENCED = "<!-- fusengine:kimi-rules:start -->\nbody\n<!-- fusengine:kimi-rules:end -->\n";
+
+/** Build a fixture kimi home dir, optionally with a fenced/unfenced AGENTS.md. */
+function kimiHome(root: string, agentsMd?: string): string {
+  const home = mkdtempSync(join(root, "kimi-home-"));
+  if (agentsMd !== undefined) writeFileSync(join(home, "AGENTS.md"), agentsMd);
+  return home;
+}
+
+/** Fixture plugin root carrying one rules file, for `injectRules`. */
+function pluginRoot(root: string): string {
+  const dir = mkdtempSync(join(root, "plugin-"));
+  mkdirSync(join(dir, "rules"), { recursive: true });
+  writeFileSync(join(dir, "rules", "00.md"), "# rules\nbody\n");
+  return dir;
+}
+
+describe("rulesInAgentsMd", () => {
+  const root = mkdtempSync(join(tmpdir(), "kimi-notice-only-"));
+
+  test("fences present -> true", () => {
+    expect(rulesInAgentsMd(kimiHome(root, FENCED))).toBe(true);
+  });
+
+  test("fences absent -> false", () => {
+    expect(rulesInAgentsMd(kimiHome(root, "# AGENTS.md\nplain body\n"))).toBe(false);
+  });
+
+  test("AGENTS.md absent -> false", () => {
+    expect(rulesInAgentsMd(kimiHome(root))).toBe(false);
+  });
+
+  afterAll(() => rmSync(root, { recursive: true, force: true }));
+});
+
+describe("injectRules: kimi notice-only gate", () => {
+  const root = mkdtempSync(join(tmpdir(), "kimi-notice-only-inject-"));
+  const prevKimiHome = process.env.KIMI_CODE_HOME;
+
+  afterEach(() => {
+    if (prevKimiHome === undefined) delete process.env.KIMI_CODE_HOME;
+    else process.env.KIMI_CODE_HOME = prevKimiHome;
+  });
+
+  test("kimi UserPromptSubmit, fences present -> notice only", () => {
+    process.env.KIMI_CODE_HOME = kimiHome(root, FENCED);
+    expect(injectRules(pluginRoot(root), "UserPromptSubmit", "kimi")).toBe("rules 00-08 injected");
+  });
+
+  test("kimi UserPromptSubmit, fences absent -> full corpus", () => {
+    process.env.KIMI_CODE_HOME = kimiHome(root, "# AGENTS.md\nplain\n");
+    const out = injectRules(pluginRoot(root), "UserPromptSubmit", "kimi");
+    expect(out).toContain("# rules\nbody");
+    expect(out).toContain("rules 00-08 injected");
+  });
+
+  test("kimi SessionStart, fences present -> full corpus (never gated)", () => {
+    process.env.KIMI_CODE_HOME = kimiHome(root, FENCED);
+    expect(injectRules(pluginRoot(root), "SessionStart", "kimi")).toContain("# rules\nbody");
+  });
+
+  test("kimi SubagentStart, fences present -> full corpus (never gated)", () => {
+    process.env.KIMI_CODE_HOME = kimiHome(root, FENCED);
+    expect(injectRules(pluginRoot(root), "SubagentStart", "kimi")).toContain("# rules\nbody");
+  });
+
+  test("claude-code UserPromptSubmit is unaffected by the kimi gate", () => {
+    process.env.KIMI_CODE_HOME = kimiHome(root, FENCED);
+    const out = injectRules(pluginRoot(root), "UserPromptSubmit", "claude-code");
+    expect(out).toContain("additionalContext");
+    expect(out).toContain("# rules\\nbody");
+  });
+
+  afterAll(() => rmSync(root, { recursive: true, force: true }));
+});