[witbrock]

Merge decision: ready — both conversation renderers offer the same accessible latest-message control, distinct from first-unread/new navigation, with viewport preservation and visible-read regression evidence.

User outcome

Messages previously showed a rectangular “New messages” end-navigation button only after refresh, while chat offered a circular arrow whenever scrolled away. Both now use a shared 44px circular “Scroll to latest message” button with keyboard focus transfer. First-unread/new navigation remains semantically separate.

Task: #V#task_agent_63185986b5f7204bf1c718922c4a54f4.

Material changes

Messages starts at the first loaded unread contribution, preserves position on explicit/background refresh and pagination, and disconnects read observers during rendering. Visible-read observation excludes content behind the mobile composer. Chat retains the first new-arrival boundary across successive arrivals. Shared controls occupy composer space to avoid transcript obstruction and mobile clipping.

The dated affordance audit enumerates reconciled and intentionally retained controls, sender alignment, widths, canonical read semantics, composer features and source screenshot provenance.

Evidence

• 65 targeted Jest tests across 11 suites passed (64 in the combined run; the added overlap regression passed with the 12-test message-exchange suite).
• Static ESLint for changed production/test JavaScript and git diff --check passed.
• Actual templates/modules/styles exercised by the isolated browser fixture at 1440px and 360px: four renderer/viewport cases, native Enter/Space activation, accessible names, focus, 44px hit targets, zero horizontal overflow, sender labels/alignment, unread retention, failed-read retry, pagination, refresh/reopening and badge read-back.
• Screenshots and measurements retained at /tmp/conversation-affordance-evidence on the worker. This is fixture acceptance, not authenticated-server evidence.
• Source-module frontend has no npm bundling step. Browser imports passed and the versioned git-archive release package built; SHA-256 1cdbe13cdb104a31460ed0c902bb963b6e8b1e9ac69d1c4e5993207a1db1fe77.

Ship boundary

Minimum criteria are equivalent latest navigation and observable preservation of unseen message state across the changed client paths. Broken keyboard/mobile navigation or newly clearing unseen contributions would block shipment; neither was observed. Chat retains its existing conversation-level read cursor; Messages retains per-contribution receipts. No new authentication, storage semantics, model calls, deployment or infrastructure changes are included. The initial task does not explicitly request public deployment.