fix(linkedin-studio): S4 harden multiplatform — Step-0 empty-source fallback + cross-platform buzzword line

S4 close-out (2 edits / 1 command file · lint 81/0 · counts 29/19/26/6):
- multiplatform.md:28 Step 0: empty-source fallback (drafts empty + no recent posts + nothing pasted -> stop, ask user to paste; never fabricate source)
- multiplatform.md:45 Adaptation Templates: cross-platform voice-hygiene line (banned buzzwords = content rule #4; adaptation rewrites can introduce them)

Class call: NOT post-emitting (output is Twitter/slides/YouTube) -> no LinkedIn predicate imposed; tested as guided/cross-format + routing sub-predicate. Routing (/linkedin:newsletter) + both reference files resolve; no subagents. Axis-c (buzzword) + axis-d (degradation) closed; axes a/b PASS. Local-only per push policy.

docs/hardening/log.md

@@ -386,3 +386,80 @@ perspective *extending* the source, not echoing it — the commodity-reaction gu
 - Disposition: **HARDENED** (3 edits, axis-c + axis-d) · 0 deferrals · axes a/b PASS.
 
 ---
+
+## Session 4 — Create III (`multiplatform`)
+
+> S4 status: re-grounded the proposed predicates against the actual `multiplatform.md` lines
+> BEFORE talk (jerndisiplin: assert-after-read). Field-notes inbox **absent** at S4 → graceful
+> no-op (SC-I). All `file:line` below are tool-grounded against the FINAL (post-edit) file.
+> **Class call (operator-agreed):** NOT post-emitting — output is Twitter/slides/YouTube, so the
+> LinkedIn content predicates (hook 110–140, length band, no-body-link, topic→5 pillars) do **not**
+> apply per platform; imposing them here would be the exact category error the Create-III brief warns
+> against. Tested as **guided/cross-format with a routing sub-predicate**.
+
+### /linkedin:multiplatform — adapt existing LinkedIn content to short-/cross-format (Twitter thread · slides · YouTube script)
+
+**INTENT.** `multiplatform` is the Create journey's **cross-format adapter**: take existing LinkedIn
+content and re-shape it for other platforms (Twitter/X thread, presentation slides, YouTube script) —
+*write once, publish everywhere*. It explicitly does **not** own long-form (newsletters / blog / essays
+→ `/linkedin:newsletter`, the single long-form entry point). It is an *adapter*, not a post-generator:
+the value-add is adaptation fidelity (each platform's own rules) + correct routing of out-of-scope
+(long-form) requests, not LinkedIn-feed quality gating.
+
+**SIMULATE.**
+- **Persona (ICP):** the author — a finished LinkedIn post in drafts, wants to reuse it as a Twitter thread.
+- **Invocation:** `/linkedin:multiplatform` → pick "Twitter/X thread".
+- **Walk:** Step 0 (`:21`) load source from `drafts/` + state → Step 1 (`:31`) AskUserQuestion pick
+  Twitter → Twitter template (`:53`, hook ≤**280** + 🧵 + one-idea tweets + CTA) → Step 2 (`:115`) save
+  `drafts/multiplatform/twitter-[slug].md` (`:118`) + clipboard, "Copied" (`:123`). **Promised artifact
+  produced.**
+- **CONCRETE friction (axis d, adapter-specific — anchored, not a generated post):** `grep` for an
+  empty-source / fabrication guard in Step 0 → only matched l.23 "Ask the user to provide … or read
+  from drafts" — **no fallback** for the case where drafts is empty/absent, state has no recent posts,
+  AND the user pasted nothing. Risk: the model **fabricates a LinkedIn post to adapt** rather than
+  stopping. (Same failure class as S3's WebFetch-no-extraction gap.)
+- **Second friction (axis c, voice hygiene):** the banned-buzzword list (content rule #4) is
+  *platform-agnostic voice hygiene*, not a char rule — and adaptation **rewrites** the source
+  (condense the hook to 280, expand to a script), which can introduce buzzwords absent from the
+  clean source. Pre-edit the file mentioned buzzwords **nowhere** (full read). Operator-judged in
+  scope (light line, not a full gate).
+
+**EVALUATE (4 axes).**
+- **(a) intention fidelity — PASS.** Three adapters (Twitter/slides/YouTube), source-loading,
+  save + clipboard, long-form correctly delegated — delivers the description's promise.
+- **(b) algorithm/platform bar — PASS.** Per-platform rules correct, **no LinkedIn-rule leak**:
+  Twitter "280 chars max" (`:53`); **no** `110`/`140` hook band anywhere in the file (grep NONE —
+  the desired result for a non-LinkedIn surface). Long-form routing intact (see (c)).
+- **(c) MECHANICAL predicate (routing sub-predicate) — PASS; voice-hygiene sub-gap fixed.** Every
+  emitted `/linkedin:newsletter` (`:6/:34/:36/:132`) resolves to a real `commands/newsletter.md`
+  (verified, ls) ✓; both reference files resolve — `references/linkedin-formats.md` (`:128`) +
+  `engagement-frameworks.md` (`:129`) (verified, ls) ✓. **Buzzword voice-hygiene line absent** →
+  added (`:45`).
+- **(d) agent-wiring + graceful degradation — wiring N/A; degradation GAP → fixed.** No subagents
+  invoked (`grep subagent_type` → NONE — nothing to resolve). **Graceful degradation:** no
+  empty-source/fabrication guard in Step 0 (grep matched only the weak "ask … or read from drafts")
+  → added a stop-and-ask-never-fabricate fallback (`:28`).
+
+**HARDEN (surgical — 2 edits, 1 file, both grep-confirmed landed).**
+- `commands/multiplatform.md:28` — **added** Step-0 empty-source fallback: *"If none of these yields
+  source content (empty/absent drafts, no recent posts, and nothing pasted), **stop and ask the user
+  to paste the LinkedIn post to adapt** — never fabricate source content to adapt."*
+- `commands/multiplatform.md:45` — **added** an "Adaptation Templates" voice-hygiene blockquote:
+  *"adaptation rewrites the source — keep the adapted copy free of the banned corporate buzzwords
+  (content rule #4: leverage, synergy, paradigm shift, thought leader, disruptive, value proposition,
+  ecosystem, holistic approach) on every platform; don't let the rewrite introduce them."*
+- **Deferrals:** none. **Scope note (flagged, not touched):** Step 2's "Copied to clipboard." (`:123`)
+  is unconditional, but `clipboard-helper.mjs` is shared, tested infra used identically by ~9 content
+  commands — re-gating it here would be scope-creep into a shared pattern (surgical discipline).
+
+**VERIFY.**
+- `bash scripts/test-runner.sh` → `Passed: 81 · Failed: 0 · Warnings: 0`; counts **29/19/26/6**
+  unchanged (`ls commands/*.md|wc -l` == 29, `ls agents/*.md|wc -l` == 19; `git diff --stat` =
+  `multiplatform.md` only, +9 insertions, 0 deletions).
+- Before/after delta: axis (d) empty-source now degrades to "paste the post / never fabricate"
+  instead of an invented source; axis (c) the rewrite is now bound by the banned-buzzword list on
+  every platform. The 2 edits are the cause.
+- Disposition: **HARDENED** (2 edits, axis-c + axis-d) · 0 deferrals · axes a/b PASS · class
+  confirmed non-post-emitting (no LinkedIn predicate imposed).
+
+---