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/ui/tui/src/chat/helpers.ts

@@ -109,6 +109,10 @@ export function transcriptToolCallIds(session: Session): Set<string> {
  * rather than the shape of the replacement. Other replacements (a pruned
  * `tool/result`, a regenerated `assistant/message`) rewrite one node for the
  * model and mark no boundary in the conversation.
+ *
+ * The replacement check is redundant at both current call sites, which already
+ * reached a replacement: it keeps the exported predicate true to its name for a
+ * third caller, rather than making that caller repeat the check.
  * @param event - event to test.
  * @returns true when the event compacted a surface range.
  */

packages/ui/tui/src/index.ts

@@ -836,6 +836,12 @@ export function createTuiChat(
    * surface shadows compacted ranges, so it is not the source here: every
    * append-origin message stays rendered, and a replacement contributes at most
    * the compaction marker at its own log position.
+   *
+   * The `tool/call` pairing check has no live counterpart, because only replay
+   * can meet an orphan: `tool/call` carries no `surfaceOp` of its own, so it
+   * inherits transcript membership from the `assistant/message` that advertised
+   * it, which the live listener has necessarily just rendered. A loaded log is a
+   * replay boundary, so the pairing is re-derived here instead of assumed.
    */
   const rebuildTranscript = (populateHistory: boolean): void => {
     chat.clear()