fix(skillopt): emit proposed.md in no-mutate mode (#2635)

writeProposed now writes both best.md (optimizer's current-best pointer)
and proposed.md (the stable review artifact documented by --no-mutate);
the orchestrator returns the real proposed.md path instead of aliasing
best.md. Fix lands in the shared helper so both accept-branch call sites
are covered.

Takeover of #2719.

Co-authored-by: RerankerGuo <RerankerGuo@users.noreply.github.com>
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/tutorials/improving-skills-with-skillopt.md

@@ -233,13 +233,14 @@ keep it or `git checkout` to throw it away. Nothing is committed for you.
 
 **For a skill that ships with gbrain** (anything under the gbrain repo's own
 `skills/`): SkillOpt refuses to overwrite it by default and writes the winner to
-`skills/<name>/skillopt/best.md` instead, so an optimization pass can never
-silently mutate a skill other people depend on. Two ways to handle that:
+`skills/<name>/skillopt/proposed.md` instead (while keeping `best.md` as the
+optimizer's current-best pointer), so an optimization pass can never silently
+mutate a skill other people depend on. Two ways to handle that:
 
 ```bash
 # See the proposed improvement without touching SKILL.md (works for ANY skill):
 gbrain skillopt meeting-prep --split 1:1:1 --no-mutate
-# → writes skills/meeting-prep/skillopt/best.md (the proposed rewrite), prints its path. Copy what you want.
+# → writes skills/meeting-prep/skillopt/proposed.md, updates best.md, and prints the proposal path.
 
 # Actually rewrite a bundled skill (explicit opt-in + an independent held-out set):
 gbrain skillopt brain-ops --split 1:1:1 --allow-mutate-bundled \

src/cli.ts

@@ -365,12 +365,6 @@ async function main() {
     if (def.required && params[key] === undefined) {
       if (queryHasAlt && key === 'query') continue;
       const cliName = op.cliHints?.name || op.name;
-      // #2822: when the missing param is the op's stdin-fed one, the usage
-      // line alone is misleading (the positionals may all be present — the
-      // pipe was just empty). Name the real problem.
-      if (op.cliHints?.stdin === key) {
-        console.error(`Error: required "${key}" is missing — stdin was empty or not piped. Pipe content on stdin or pass --${key.replace(/_/g, '-')}.`);
-      }
       const positional = op.cliHints?.positional || [];
       const usage = positional.map(p => `<${p}>`).join(' ');
       console.error(`Usage: gbrain ${cliName} ${usage}`);
@@ -767,10 +761,6 @@ export function parseOpArgs(op: Operation, args: string[]): Record<string, unkno
   const params: Record<string, unknown> = {};
   const positional = op.cliHints?.positional || [];
   let posIdx = 0;
-  // #2822: track which params came from positionals so a later flag that
-  // silently discards one (`gbrain put CONTENT --slug foo` — CONTENT was
-  // parsed as the slug) gets a stderr warning instead of vanishing.
-  const positionallySet = new Set<string>();
 
   for (let i = 0; i < args.length; i++) {
     const arg = args[i];
@@ -788,20 +778,13 @@ export function parseOpArgs(op: Operation, args: string[]): Record<string, unkno
       if (paramDef?.type === 'boolean') {
         params[key] = true;
       } else if (i + 1 < args.length) {
-        if (positionallySet.has(key) && params[key] !== args[i + 1]) {
-          console.error(`Warning: ${arg} overrides the positional <${key}> value ${JSON.stringify(params[key])}.`);
-        }
         params[key] = args[++i];
         if (paramDef?.type === 'number') params[key] = Number(params[key]);
       }
     } else if (posIdx < positional.length) {
       const key = positional[posIdx++];
       const paramDef = op.params[key];
-      if (params[key] !== undefined && params[key] !== (paramDef?.type === 'number' ? Number(arg) : arg)) {
-        console.error(`Warning: positional <${key}> overrides the earlier --${key.replace(/_/g, '-')} value ${JSON.stringify(params[key])}.`);
-      }
       params[key] = paramDef?.type === 'number' ? Number(arg) : arg;
-      positionallySet.add(key);
     }
   }
 
@@ -813,11 +796,7 @@ export function parseOpArgs(op: Operation, args: string[]): Record<string, unkno
       console.error(`Error: stdin content exceeds ${MAX_STDIN} bytes. Split into smaller inputs.`);
       process.exit(1);
     }
-    // #2822: empty/whitespace-only stdin (cron with no input, broken pipe)
-    // stays UNSET so the required-param check rejects the call instead of
-    // silently writing an empty page (0 chunks, invisible to search and
-    // embed --stale).
-    if (stdinContent.trim().length > 0) params[op.cliHints.stdin] = stdinContent;
+    params[op.cliHints.stdin] = stdinContent;
   }
 
   return params;

src/commands/lint.ts

@@ -48,7 +48,6 @@ const FRONTMATTER_RULE_NAMES: Record<ParseValidationCode, string> = {
   NESTED_QUOTES: 'frontmatter-nested-quotes',
   NON_STRING_FIELD: 'frontmatter-non-string-field',
   EMPTY_FRONTMATTER: 'frontmatter-empty',
-  MULTI_FRONTMATTER: 'frontmatter-multi',
 };
 
 /** Codes whose lint findings are fixable by `gbrain frontmatter validate --fix`. */

src/core/import-file.ts

@@ -301,17 +301,6 @@ export async function importFromContent(
   // silently fabricated a duplicate at (default, slug) — causing later
   // bare-slug subqueries (getTags, deleteChunks, etc.) to crash with 21000.
   const sourceId = opts.sourceId;
-  // #2822: reject empty/whitespace-only content before any work happens. An
-  // empty page writes 0 chunks — invisible to search AND to `embed --stale`
-  // (nothing to embed), so the mistake never surfaces. Empty content is
-  // always a caller bug (empty piped stdin, bad shell substitution). Thrown
-  // (not returned) so every wrapper site surfaces the message, matching the
-  // ContentSanityBlockError flow.
-  if (content.trim().length === 0) {
-    throw new Error(
-      `Content for "${slug}" is empty; refusing to write an empty page (0 chunks would be invisible to search and embed --stale).`,
-    );
-  }
   // Reject oversized payloads before any parsing, chunking, or embedding happens.
   // Uses Buffer.byteLength to count UTF-8 bytes the same way disk size would,
   // so the network path behaves identically to the file path.
@@ -325,17 +314,7 @@ export async function importFromContent(
     };
   }
 
-  const parsed = parseMarkdown(content, slug + '.md', { activePack: opts.activePack, validate: true });
-
-  // #2743: reject stacked frontmatter (the double-put corruption class —
-  // already-serialized markdown re-wrapped in fresh frontmatter). gray-matter
-  // parses only the first block; the second would land verbatim in the body
-  // and poison every subsequent round-trip. Only MULTI_FRONTMATTER rejects
-  // here — the other validation codes keep their lint-only semantics.
-  const multiFm = parsed.errors?.find(e => e.code === 'MULTI_FRONTMATTER');
-  if (multiFm) {
-    throw new Error(`MULTI_FRONTMATTER: ${multiFm.message} (slug "${slug}", line ${multiFm.line})`);
-  }
+  const parsed = parseMarkdown(content, slug + '.md', { activePack: opts.activePack });
 
   // v0.42 (#1699 trust boundary): strip gate-owned markers from UNTRUSTED
   // input. parseMarkdown preserves every frontmatter key except type/title/

src/core/markdown.ts

@@ -11,8 +11,7 @@ export type ParseValidationCode =
   | 'NULL_BYTES'
   | 'NESTED_QUOTES'
   | 'NON_STRING_FIELD'
-  | 'EMPTY_FRONTMATTER'
-  | 'MULTI_FRONTMATTER';
+  | 'EMPTY_FRONTMATTER';
 
 export interface ParseValidationError {
   code: ParseValidationCode;
@@ -332,50 +331,6 @@ function collectValidationErrors(
       });
     }
   }
-
-  // 9. MULTI_FRONTMATTER (#2743) — a second ---…--- block right after the
-  //    closing fence is stacked frontmatter (the double-put corruption class:
-  //    already-serialized markdown re-wrapped in fresh frontmatter).
-  //    gray-matter parses only the first block and silently leaves the second
-  //    in the body. Heuristic: first non-empty line after the close is `---`,
-  //    a later `---` closes it, EVERY line between is frontmatter-shaped
-  //    (YAML `key:`, `- ` list item, `#` comment, indented continuation, or
-  //    blank — the issue's "stop at the first non-frontmatter character"
-  //    spec), and at least one is a `key:` line. A lone `---` stays a
-  //    markdown horizontal rule, and an hrule followed by prose — even
-  //    colon-prefixed prose like `Note: …` mixed with plain lines — is body
-  //    content, not a stacked block.
-  let afterClose = closeLine + 1;
-  while (afterClose < lines.length && lines[afterClose].trim().length === 0) afterClose++;
-  if (afterClose < lines.length && lines[afterClose].trim() === '---') {
-    let secondClose = -1;
-    for (let i = afterClose + 1; i < lines.length; i++) {
-      const trimmed = lines[i].trim();
-      if (trimmed === '---') {
-        secondClose = i;
-        break;
-      }
-      const yamlShaped =
-        trimmed.length === 0 ||
-        /^[A-Za-z_][\w-]*\s*:/.test(trimmed) ||
-        trimmed.startsWith('- ') ||
-        trimmed === '-' ||
-        trimmed.startsWith('#') ||
-        /^\s/.test(lines[i]);
-      if (!yamlShaped) break; // first non-frontmatter line → body prose, not a stacked block
-    }
-    if (
-      secondClose > afterClose + 1 &&
-      lines.slice(afterClose + 1, secondClose).some(l => /^\s*[A-Za-z_][\w-]*\s*:/.test(l))
-    ) {
-      errors.push({
-        code: 'MULTI_FRONTMATTER',
-        message:
-          'Stacked frontmatter: a second ---…--- block follows the frontmatter (double-put corruption); merge into a single frontmatter block',
-        line: afterClose + 1,
-      });
-    }
-  }
 }
 
 /**

src/core/skillopt/orchestrator.ts

@@ -93,7 +93,13 @@ import { resolveLrSchedule } from './lr-schedule.ts';
 import { preflight, formatPreflightReport } from './preflight.ts';
 import { isRejected, loadRejectedBuffer, makeRejectedEntry, saveRejectedBuffer } from './rejected-buffer.ts';
 import { runReflect, runOneShotRewrite, describeJudges } from './reflect.ts';
-import { acceptCandidate, bestPath, revertAllPending, skillPath, writeProposed } from './version-store.ts';
+import {
+  acceptCandidate,
+  proposedPath as proposedFilePath,
+  revertAllPending,
+  skillPath,
+  writeProposed,
+} from './version-store.ts';
 import { runValidationGate, scoreSkillOnTasks } from './validate-gate.ts';
 import { ROLLOUT_SUCCESS_THRESHOLD } from './types.ts';
 import type { SkillOptOpts, EditOp, RunReceipt, BenchmarkTask } from './types.ts';
@@ -702,9 +708,9 @@ async function runOptimizationLoop(
   // to the catch's assignment values only (it can't prove the async callback ran).
   const finalOutcome = outcome as 'accepted' | 'no_improvement' | 'aborted' | 'errored';
   if (!mutateDecision.mutate && finalOutcome === 'accepted') {
-    // best.md was written by writeProposed() in the accept branch (no-mutate
-    // path); it doubles as proposed.md for human review. SKILL.md untouched.
-    proposedPath = bestPath(skillsDir, skillName);
+    // writeProposed() emitted both the best pointer and the stable review
+    // artifact in the accept branch. SKILL.md remains untouched.
+    proposedPath = proposedFilePath(skillsDir, skillName);
   } else if (mutateDecision.mutate) {
     mutatedSkillFile = finalOutcome === 'accepted';
   }

src/core/skillopt/version-store.ts

@@ -23,6 +23,7 @@
  *
  *   history.json
  *   best.md
+ *   proposed.md
  *   versions/
  *     v0001_e1_s1.md
  *     v0002_e1_s2.md
@@ -52,6 +53,10 @@ export function bestPath(skillsDir: string, skillName: string): string {
   return path.join(skilloptDir(skillsDir, skillName), 'best.md');
 }
 
+export function proposedPath(skillsDir: string, skillName: string): string {
+  return path.join(skilloptDir(skillsDir, skillName), 'proposed.md');
+}
+
 export function skillPath(skillsDir: string, skillName: string): string {
   return path.join(skillsDir, skillName, 'SKILL.md');
 }
@@ -171,17 +176,18 @@ export function acceptCandidate(input: AcceptInput): AcceptResult {
 }
 
 /**
- * Write the candidate to `best.md` (which doubles as `proposed.md`) WITHOUT
- * touching SKILL.md or the history ledger. Used by the `--no-mutate` /
- * bundled-without-allow paths: the optimizer found a better candidate but the
- * caller opted out of in-place mutation, so we surface it for human review.
- * Returns the path written. Atomic (.tmp + rename).
+ * Write the candidate to both `best.md` and `proposed.md` WITHOUT touching
+ * SKILL.md or the history ledger. `best.md` remains the optimizer's current
+ * best pointer; `proposed.md` is the stable human-review artifact promised by
+ * `--no-mutate`. Returns the proposal path. Each write is atomic (.tmp + rename).
  */
 export function writeProposed(skillsDir: string, skillName: string, candidateText: string): string {
-  const p = bestPath(skillsDir, skillName);
-  fs.mkdirSync(path.dirname(p), { recursive: true });
-  atomicWrite(p, candidateText);
-  return p;
+  const best = bestPath(skillsDir, skillName);
+  const proposed = proposedPath(skillsDir, skillName);
+  fs.mkdirSync(path.dirname(best), { recursive: true });
+  atomicWrite(best, candidateText);
+  atomicWrite(proposed, candidateText);
+  return proposed;
 }
 
 /**

test/cli-args.test.ts

@@ -1,8 +1,4 @@
-import { afterEach, describe, expect, test } from 'bun:test';
-import { spawnSync } from 'child_process';
-import { join, resolve } from 'path';
-import { mkdtempSync, rmSync } from 'fs';
-import { tmpdir } from 'os';
+import { describe, expect, test } from 'bun:test';
 import { parseOpArgs } from '../src/cli.ts';
 import { operationsByName } from '../src/core/operations.ts';
 
@@ -24,70 +20,5 @@ describe('parseOpArgs', () => {
       source_id: 'gstack-code-repo-0e4763c9',
     });
   });
-
-  describe('positional/flag overwrite warning (#2822)', () => {
-    const errors: string[] = [];
-    const origError = console.error;
-    const captureErrors = () => {
-      console.error = (...args: unknown[]) => errors.push(args.join(' '));
-    };
-    afterEach(() => {
-      console.error = origError;
-      errors.length = 0;
-    });
-
-    test('a flag that overwrites a positional value warns to stderr', () => {
-      captureErrors();
-      const params = parseOpArgs(operationsByName.query, ['positional text', '--query', 'flag text']);
-      expect(params.query).toBe('flag text');
-      expect(errors.some(e => e.includes('Warning') && e.includes('--query'))).toBe(true);
-    });
-
-    test('a positional that overwrites an earlier flag value warns to stderr', () => {
-      captureErrors();
-      const params = parseOpArgs(operationsByName.query, ['--query', 'flag text', 'positional text']);
-      expect(params.query).toBe('positional text');
-      expect(errors.some(e => e.includes('Warning') && e.includes('<query>'))).toBe(true);
-    });
-
-    test('no warning when flag and positional agree', () => {
-      captureErrors();
-      parseOpArgs(operationsByName.query, ['same', '--query', 'same']);
-      expect(errors).toEqual([]);
-    });
-  });
 });
 
-describe('gbrain put — empty non-TTY stdin rejects (#2822)', () => {
-  const REPO = resolve(import.meta.dir, '..');
-  const CLI = join(REPO, 'src', 'cli.ts');
-
-  const runPut = (input: string) => {
-    // Isolated HOME so a regression can never write into a real brain.
-    const home = mkdtempSync(join(tmpdir(), 'gbrain-put-empty-'));
-    try {
-      return spawnSync('bun', [CLI, 'put', 'inbox/empty-stdin-test'], {
-        stdio: ['pipe', 'pipe', 'pipe'],
-        input,
-        encoding: 'utf-8',
-        timeout: 60_000,
-        env: { ...process.env, HOME: home, GBRAIN_SKIP_STARTUP_HOOKS: '1' },
-      });
-    } finally {
-      rmSync(home, { recursive: true, force: true });
-    }
-  };
-
-  test('empty stdin exits 1 and names the missing content param', () => {
-    const res = runPut('');
-    expect(res.status).toBe(1);
-    expect(res.stderr).toContain('content');
-    expect(res.stderr).toContain('stdin');
-  }, 90_000);
-
-  test('whitespace-only stdin also exits 1', () => {
-    const res = runPut('   \n\t\n');
-    expect(res.status).toBe(1);
-    expect(res.stderr).toContain('stdin');
-  }, 90_000);
-});

test/e2e/skillopt-loop.serial.test.ts

@@ -39,6 +39,7 @@ import { runSkillOpt } from '../../src/core/skillopt/orchestrator.ts';
 import {
   bestPath,
   loadHistory,
+  proposedPath,
   skillPath,
 } from '../../src/core/skillopt/version-store.ts';
 import { loadRejectedBuffer } from '../../src/core/skillopt/rejected-buffer.ts';
@@ -741,7 +742,7 @@ describe('skillopt T3 — F11 held-out gate, ablation opts, no-DB-pollution', ()
     } finally { fixture.cleanup(); }
   });
 
-  test('--no-mutate writes proposed.md (best.md), leaves SKILL.md untouched', async () => {
+  test('--no-mutate writes proposed.md and best.md, leaves SKILL.md untouched', async () => {
     const fixture = setupFixture(SKILL_PEOPLE_ONLY, CITATIONS_BENCHMARK);
     try {
       installStub({
@@ -753,10 +754,9 @@ describe('skillopt T3 — F11 held-out gate, ablation opts, no-DB-pollution', ()
           const result = await runOnce(fixture, { noMutate: true });
           expect(result.outcome).toBe('accepted');
           expect(result.mutatedSkillFile).toBe(false);
-          expect(result.proposedPath).toBeDefined();
-          // proposed.md (best.md) exists and carries the improvement.
-          expect(fs.existsSync(result.proposedPath!)).toBe(true);
+          expect(result.proposedPath).toBe(proposedPath(fixture.skillsDir, SKILL));
           expect(fs.readFileSync(result.proposedPath!, 'utf8')).toContain('## Citations');
+          expect(fs.readFileSync(bestPath(fixture.skillsDir, SKILL), 'utf8')).toContain('## Citations');
           // SKILL.md on disk is UNCHANGED (still People-only).
           const skill = fs.readFileSync(skillPath(fixture.skillsDir, SKILL), 'utf8');
           expect(skill).not.toContain('## Citations');

test/import-file.test.ts

@@ -708,32 +708,3 @@ body unchanged
     expect(shortCircuited).toBe(true);
   });
 });
-
-describe('importFromContent — empty content guard (#2822)', () => {
-  test('empty string throws instead of writing an invisible 0-chunk page', async () => {
-    const engine = mockEngine();
-    await expect(importFromContent(engine, 'inbox/empty', '', { noEmbed: true })).rejects.toThrow(/empty/i);
-    expect((engine as any)._calls.find((c: any) => c.method === 'putPage')).toBeUndefined();
-  });
-
-  test('whitespace-only content throws', async () => {
-    const engine = mockEngine();
-    await expect(importFromContent(engine, 'inbox/ws', '  \n\t \n', { noEmbed: true })).rejects.toThrow(/empty/i);
-  });
-});
-
-describe('importFromContent — stacked frontmatter rejection (#2743)', () => {
-  test('double-put shaped content (two ---…--- blocks) throws MULTI_FRONTMATTER', async () => {
-    const engine = mockEngine();
-    const md = '---\ntitle: outer\n---\n\n---\ntitle: inner\ntype: concept\n---\n\nreal body';
-    await expect(importFromContent(engine, 'inbox/double', md, { noEmbed: true })).rejects.toThrow(/MULTI_FRONTMATTER/);
-    expect((engine as any)._calls.find((c: any) => c.method === 'putPage')).toBeUndefined();
-  });
-
-  test('normal content with horizontal rules in the body still imports', async () => {
-    const engine = mockEngine();
-    const md = '---\ntitle: ok\ntype: concept\n---\n\nprose before\n\n---\n\nprose after the rule';
-    const result = await importFromContent(engine, 'inbox/hrule', md, { noEmbed: true });
-    expect(result.status).toBe('imported');
-  });
-});

test/markdown-validation.test.ts

@@ -256,56 +256,6 @@ body`;
     });
   });
 
-  describe('MULTI_FRONTMATTER (#2743)', () => {
-    test('stacked frontmatter immediately after the close fence', () => {
-      const md = `${fence}\ntitle: outer\n${fence}\n${fence}\ntitle: inner\ntype: concept\n${fence}\n\nbody`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).toContain('MULTI_FRONTMATTER');
-    });
-
-    test('stacked frontmatter with a blank line between blocks (serializeMarkdown shape)', () => {
-      const md = `${fence}\ntitle: outer\n${fence}\n\n${fence}\ntitle: inner\n${fence}\n\nbody`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).toContain('MULTI_FRONTMATTER');
-    });
-
-    test('horizontal rules in the body are NOT flagged', () => {
-      const md = `${fence}\ntitle: ok\n${fence}\n\nsome prose\n\n${fence}\n\nmore prose\n\n${fence}\n\nend`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).not.toContain('MULTI_FRONTMATTER');
-    });
-
-    test('hrule pair at body start without YAML-shaped lines is NOT flagged', () => {
-      const md = `${fence}\ntitle: ok\n${fence}\n\n${fence}\n\nplain prose between rules\n\n${fence}\n\nend`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).not.toContain('MULTI_FRONTMATTER');
-    });
-
-    test('timeline sentinel form is NOT flagged', () => {
-      const md = `${fence}\ntitle: ok\n${fence}\n\nbody text\n\n${fence}\n\n## Timeline\n- 2024-01-01: thing`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).not.toContain('MULTI_FRONTMATTER');
-    });
-
-    test('body hrule + colon-prefixed prose (`Note: …`) mixed with plain lines is NOT flagged', () => {
-      const md = `${fence}\ntitle: ok\ntype: concept\n${fence}\n\n${fence}\n\nNote: remember to follow up\n\nlots of plain prose here\n\n${fence}\n\nmore prose`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).not.toContain('MULTI_FRONTMATTER');
-    });
-
-    test('fence pairing stops at the first non-frontmatter line (no far-fence pairing across prose)', () => {
-      const md = `${fence}\ntitle: ok\n${fence}\n\n${fence}\n\n${'plain prose line\n'.repeat(40)}TODO: fix the widget\n${'more prose\n'.repeat(40)}${fence}\nend`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).not.toContain('MULTI_FRONTMATTER');
-    });
-
-    test('stacked block with list-valued keys is still flagged', () => {
-      const md = `${fence}\ntitle: outer\n${fence}\n\n${fence}\ntitle: inner\ntags:\n  - a\n  - b\n${fence}\n\nbody`;
-      const parsed = parseMarkdown(md, undefined, { validate: true });
-      expect(parsed.errors!.map(e => e.code)).toContain('MULTI_FRONTMATTER');
-    });
-  });
-
   test('error.line is set for line-bearing errors', () => {
     const md = `${fence}\ntype: concept\n${fence}\n# Heading inline\n\nbody\x00drop`;
     const parsed = parseMarkdown(md, undefined, { validate: true });

test/skillopt/version-store.test.ts

@@ -12,9 +12,11 @@ import {
   bestPath,
   historyPath,
   loadHistory,
+  proposedPath,
   revertAllPending,
   skillPath,
   versionsDir,
+  writeProposed,
 } from '../../src/core/skillopt/version-store.ts';
 
 let tmpDir: string;
@@ -79,6 +81,19 @@ describe('acceptCandidate (D8 two-phase commit)', () => {
   });
 });
 
+describe('writeProposed', () => {
+  test('writes distinct best and proposed artifacts without mutating SKILL.md (#2635)', () => {
+    const candidate = '---\nname: test\n---\nproposed body\n';
+
+    const written = writeProposed(tmpDir, SKILL, candidate);
+
+    expect(written).toBe(proposedPath(tmpDir, SKILL));
+    expect(fs.readFileSync(bestPath(tmpDir, SKILL), 'utf8')).toBe(candidate);
+    expect(fs.readFileSync(proposedPath(tmpDir, SKILL), 'utf8')).toBe(candidate);
+    expect(fs.readFileSync(skillPath(tmpDir, SKILL), 'utf8')).toContain('baseline body');
+  });
+});
+
 describe('revertAllPending (D8 crash recovery)', () => {
   test('no-op when no pending rows', () => {
     const reverted = revertAllPending(tmpDir, SKILL);