A2A timeline on mobile: the five groups through the shared classifier #699

What

Bring the agreed A2A timeline design to mobile: the same five groups, by who is speaking, as on web. The design is the project artifact upstream-merge-2026-10-24/a2a-timeline-design.md, settled with Jackson on 2026-10-24.

• Call the shared classifier in packages/client-runtime/src/j5/, which the 2026-10-24 advance adds for web. Don't add a second parser.
• Land FORK.md's reserved "Timeline delegate" seam in apps/mobile/src/features/threads/ThreadFeed.tsx.

Why it isn't in the advance

J5 mobile is being rebuilt after this advance (Jackson, 2026-10-24). Until then, J5 deliveries on mobile fall under upstream's own fold (pingdotgg#23135). The folded preview there is probably J5's envelope header rather than the letter's first line; this is inferred, not checked on a device.

Done when

• Mobile renders all five groups from the shared classifier, and no folded row shows an envelope.
• The "Timeline delegate" seam is a numbered FORK.md case and is listed in apps/mobile/src/j5/upstreamSeams.test.ts.