Composing the title and body: evidence, teaching, and branding gates

**You MUST read references/pr-description-writing.md** in full. It defines value-first framing, sizing, program altitude (where this PR sits in a multi-PR series), related-work references (preserve existing Related: / Fixes on rewrite), the branding body rules, and the pre-apply audit. The only input it needs from this skill is the PR ref, if the mode selection identified one (description-only with a pasted URL, description update, or a confirmed existing-PR rewrite in the full workflow). If Step 1 (resolve branch and PR state) found an existing PR, pass its URL to Step 4 when rewriting so PR mode fetches the existing body. In Stack mode, Step 5 (apply and report) follows the post-submit description steps in references/stack-submit.md instead of composing one default-base body here.

Evidence decision before composition. Use artifacts the user or caller supplied, and take screenshots yourself only as references/visual-evidence.md describes. Never invent evidence, and never launch another CE skill to capture it.

1. User or caller supplied (URL, markdown image/embed, local path) — incorporate as ## Demo, ## Screenshots, or ## Evidence, and take no screenshots of what it already shows. A supplied screenshot of the UI without this change is different: it is the before image for item 4, not finished evidence.
2. User asked for evidence but supplied none — for screenshots of UI, go to item 4. For anything else (a recording, a demo), ask for the artifact or tell them to capture it with the harness and return.
3. No material observable claim (internal plumbing, type-only, pure refactor, inert docs) — skip without asking. Classify by runtime purpose, not extension (runtime agent instructions / config / product content / policy YAML is not auto-skippable as "docs").
4. Material visual claim (rendered UI a reviewer would judge faster or more correctly by seeing it), or the user asked for screenshots — read references/visual-evidence.md now and follow it. When it cannot capture, it falls back to item 5's note.
5. Otherwise (CLI, API, workflow, ranking, deploy/config behavior) — write a concise validation note of what was exercised. If a real run was impossible (credentials, paid services, deploy-only, hardware, missing setup), say so. Do not block PR creation for missing visuals; test or manual-check notes are fine. Never label test output "Demo" or "Screenshots."

Concept teaching gate before composition. Use the repo root gathered in Context, resolving it with git rev-parse --show-toplevel if you don't already have it (description-only and description-update modes can skip the Context snapshot). Then apply the ordinary-key rule below.

<!-- ce-config-layers:start --> Resolve ordinary CE yaml keys from the two repo files.

• Read <repo-root>/.compound-engineering/config.local.yaml, then config.yaml (<repo-root> = git rev-parse --show-toplevel). Missing files are skipped. Gitignore does not change resolution.
• Win with the first active (non-commented) value. For scalars, empty is unset; an invalid value continues to the next layer, then the skill default. For lists and maps, a present key — including an empty list or map — replaces the whole key.
• Do not use this rule for docs_root — that key is config.yaml only.

<!-- ce-config-layers:end -->

Only an active (non-commented) pr_teaching_section: key counts. Lines starting with # are YAML comments, and matching a commented template key would silently flip the decision. Teaching is off only when the winning active value is exactly false; a missing key or any other value → default on. The same layer order resolves pr_teaching_archive:: on only when the winning active value is exactly true, else off. A per-run archive:on|off token overrides it for this invocation.

• Gate on — judge novelty and compose per Step B2 of the reference.
• Gate off — compose without concept handling: skip the novelty judgment, the ## New concepts section, the Step 5 concept trailer and ce-explain offer, and archival entirely.

PR branding gate before composition. Branding is **off unless this invocation includes branding:on or the user explicitly asks in the current prompt to add Compound Engineering branding**; normalize that natural-language request to branding:on. branding:off forces off when branding:on is absent. If both tokens are present, stop and report the conflict rather than guessing. Pass the resolved branding decision, and whether the PR is new or existing, into Step D of the reference, which defines the body rules.

Then continue with the reference (Steps A–E, including Step B2 when the teaching gate is on). Step E must run before the body is returned.