docs: PRD 1.16 brief, library.write routes under REQ-LIB-6 (#1796, mos-1328)

docs/plans/2026-10-22_prd-1-16-brief.md

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+# PRD 1.16 brief: library.write routes under REQ-LIB-6
+
+Sage, 2026-10-22, for mos-1328. This follows `docs/plans/BRIEF-TEMPLATE.md`. Gitea #1796.
+
+## PRD 1.16 library.write routes under REQ-LIB-6 (mos-1328)
+
+### Problem
+
+Row 285 (C2-08b, #1790) adds the action `library.write` and grants it within-role to the six creative
+roles. REQ-WAIT-3 makes a new action a hard wait until a PRD version says it isn't, and REQ-WAIT-2 refuses
+a hard wait in a role file (`packages/business/src/vocabulary.mjs:68` ROUTED, `role.mjs`). PRD 1.15
+(row 282, #1787) lets creative agents write supporting docs but never routes the action. Scrooge found
+it (scrooge-285-routing-q1), and Webby confirmed it (webby-0164 B2). Mos ruled in mos-1328 that the
+routing changes the hard-waits list, so it needs a PRD version whose text Jason approves. Q223 and Q226
+don't cover it.
+
+### Owner and reviewer
+
+- Owner: Gosalyn.
+- Reviewer: Webby.
+- After: row 282 (PRD 1.15).
+
+### Files owned
+
+`docs/prd/mosaic-stack.md`, `packages/tasks/requirements.json` (the version only) and
+`packages/tasks/tests/requirements.test.mjs` (the version pin only).
+
+### What ships
+
+- A REQ-WAIT-3 note in the existing style: `library.write` was added as a hard wait and routes under
+  REQ-LIB-6 since version 1.16.
+- The bounds are in the text: creative roles only, within-role; Markdown under supporting folders a human
+  marked; never a story file; the writing agent's own live Gitea grant on the library project; one
+  commit per write by its own account, with the trailer, the notice and revert.
+- REQ-LIB-6 names the action. Status, the header, a 1.16 source line and a 1.16 note.
+- Nothing else changes. 1.15's text stays as Mos accepted it.
+
+### Out of scope
+
+The ROUTED entry and the role files (row 285). The write verbs (row 288, C2-02). The grant executor
+(row 287, C2-21).
+
+### Gate
+
+Webby approves the text. Jason says yes to the exact text, which Mos puts to him as one question
+(mos-1328 step 3), and the row doesn't land before that. `requirements.test.mjs` and every
+`scripts/test-*.sh` that reads the PRD or `requirements.json` are green on Sage's gate. Mos gets the
+landing commit.
+
+### Handoffs
+
+Every seat hands off directly (DECISIONS Q210, mos-1221). When the owner pushes a round or the reviewer
+posts a verdict, that seat messages the next seat's T3 thread and Sage's with `mcp__t3__t3_send_message`.
+Copy Mos's thread when Mos has a step. Mos has one here, the question to Jason.