fix(tui): a Host-started Turn in /side makes the copied parent transcript visible again

[Astro-Han]

What happened

A TUI side conversation is a Session copy that carries the parent's transcript. The driver hides it by recording #hiddenTranscriptThroughTurnId and filtering every transcript it hands the runner through visibleTranscriptMessages(). One path skips that filter.

packages/cli/src/runtime-host-session-driver.ts:1155 builds the attached Turn for a Host-started Turn with the raw opened.messages:

const turn = {
  sessionId,
  turnId,
  events: opened.channel.eventsForTurn(turnId),
  messages: opened.messages,   // unfiltered
  summary: projectSessionCatalogSummary(configuration.session),
} satisfies MakaAttachedSessionTurn;

Every sibling applies the filter — switchSession at line 563, the transcript-replacement subscriptions at lines 251 and 1243 — so this is the one gap rather than a deliberate exception.

packages/cli/src/pi-tui-runner.ts then replaces the visible transcript with exactly those messages when it adopts the attached Turn, so the parent conversation the user opened /side to get away from reappears in full.

Expected: /side shows only what happened inside the side conversation, on this path as on the others.

How to reproduce

1. Start the TUI on a Session that already has several Turns.
2. Run /side to open a side conversation.
3. Confirm the transcript is empty, as intended.
4. Cause a Host-started Turn to arrive on the side Session — the reattach path at runtime-host-session-driver.ts:1155, e.g. reconnecting while a Turn is running there.
5. The transcript is replaced with the copied parent transcript.

Deterministic once step 4 is reached; the difficulty is arranging a Host-started Turn rather than a client-started one.

Environment

• Maka version or commit: origin/main (present since feat(tui): add side conversation lifecycle #3759, which introduced both sides of this path)
• OS and version: platform-independent
• Surface: TUI
• Node.js version, if running from source: n/a

Logs, screenshots, or additional context

Found while reviewing #3803; not attributable to that PR — git log -S puts both the unfiltered messages: opened.messages and the runner's transcript replacement before its base commit.

The fix is to route this path through the same filter the siblings use:

messages: visibleTranscriptMessages(opened.messages, this.#hiddenTranscriptThroughTurnId),

Worth landing after #3760, which is open against the same two files.