round 1: project the web transcript from append-origin events

Replace the surface-ordered fold with a log-ordered human transcript:
append-origin surface events at their own log positions plus one marker per
landed compaction checkpoint. Command folding, the tool-call index, and the
rev-keyed memo carry over unchanged.

Removes foldDegraded, the padding sentinels, baseSeq, and degradedSeqs() --
they existed only to satisfy the core fold's seq === index assertion. That
also closes the pagination hole A1 exposed: a page can carry a checkpoint
whose shadowed range fell outside the window, and nothing resolves
surfaceOp.start anymore.

packages/client/test-runtime/src/fixtures.ts

@@ -46,7 +46,6 @@ export function conversationSnapshot(sessionId: SessionId): ConversationSnapshot
   return {
     sessionId,
     nodes: [],
-    foldDegraded: false,
     partial: null,
     runningCalls: [],
     codeDispatches: new Map(),