fix(tui,host): pin replayed compaction and correct projection wording

Review follow-ups on the append-origin transcript projection.
The live/replay equivalence claim was stated unconditionally but does not
cover `tool/call`: only replay re-derives call pairing, because a call
event carries no `surfaceOp` of its own and inherits transcript
membership from the `assistant/message` that advertised it — which the
live listener has necessarily just rendered. Narrow the claim in the TUI
README and Agent Note, and record at `rebuildTranscript` why the filter
is replay-only rather than a missing live branch.
Add `surface-replayed-compaction`: the three existing fixtures all come
from the live path, leaving the resume case the bug report leads with
pinned only by a unit test. The new checkpoint mounts with the
replacement already stored and records byte-identical to
`surface-after-compaction-wide`, so the two fixtures now pin the
equivalence they assert. The shared fixture appends move into
`appendPreCompactionLog` / `appendCompactionCheckpoint`.
`MESSAGE_TYPES` is not "human message event types" — it includes
`assistant/message`. Say what the code distinguishes (append-origin
conversation messages vs. model-only replacement copies) at the const,
the `paginate` and `session.history` JSDoc, the apiproxy README, and the
Agent Note.
Also: spell the replace shape as `Extract<SurfaceOp, { op: 'replace' }>`
for symmetry with the module's two other uses; document why
`isCompactCheckpoint` keeps a replacement check that is redundant at both
call sites; say that Ctrl+R toggles reasoning, which rebuilds the
transcript; and qualify "the sole source of derived history" as derived
*model* history now that the transcript is the other projection.

packages/core/session/src/index.ts

@@ -461,7 +461,8 @@ export class Session {
    *   the ordered surface; `sourceEventSeqs` records provenance (the seq
    *   numbers of events this one derives from). REQUIRED for
    *   {@link SurfaceEventType} events (every message-producing event must
-   *   declare how it joins the surface, the sole source of derived history) and
+   *   declare how it joins the surface, the sole source of derived model
+   *   history) and
    *   rejected by the compiler for non-surface types like `turn/start` or
    *   `assistant/chunk`.
    * @returns the logged event — its assigned `seq`/`time` plus the SNAPSHOT of

packages/core/session/src/surface.ts

@@ -63,7 +63,7 @@ export function isAppendSurfaceEvent(
  */
 export function isReplacementSurfaceEvent(
   event: SessionEvent,
-): event is SurfaceEvent & { surfaceOp: { op: 'replace'; start: number; end: number } } {
+): event is SurfaceEvent & { surfaceOp: Extract<SurfaceOp, { op: 'replace' }> } {
   return isSurfaceEvent(event) && event.surfaceOp !== 'append'
 }