#20717 Revert the agent pane's session-list pages: the host policy refuses them (cx-ibngi)

cx-ibngi (P1): #20644 broke local agent chats on feat.

What happened

#20644 made the pane send _acpmux/watch {enabled, limit} and _acpmux/sessions {limit, cursor}. The native pane policy (AcpmuxPaneMethods.knownParams) allows only {enabled} on watch, and does not list _acpmux/sessions at all. So the host refused both ("Refused by the cmux host"), the pane got no sessions, and the restore-journey agent rows broke too. My browser tests ran the page against a stand-in daemon without the native host, so they could not see the refusal.

What changes

This reverts #20644 (738cd81fe3f7a), the page side only. The pane sends _acpmux/watch {enabled} again and reads the whole list, exactly as before #20644. The daemon side (#20628) stays: it pages only when asked.

Paging returns in a follow-up, together with:

• the pane policy change, in Swift and in the Rust cmux-agent-pane-policy mirror, with its allowlist test;
• _acpmux/sessions scoped on the remote wire like watch;
• a parity check that covers sessionPages.ts. tests/typescript.rs scans only this.request calls in direct.ts, which is how this slipped through.

Evidence

• It is a clean git revert. The resulting page code equals the code that was green on feat before #20644.
• The private builder is out of disk right now, so this PR's CI is the verification.

Changelog

none

🤖 Generated with Claude Code

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}

---

Summary by cubic

Reverts #20644's paging of the session list because the native host policy refuses the limit param on _acpmux/watch and the _acpmux/sessions method, which broke local agent chats.

The pane now sends _acpmux/watch {enabled} again and reads the whole list as before. The daemon-side paging stays; paging returns in a follow-up with the policy changes needed on both host sides.

Migration

• The pane-side sessionPages.ts module and its browser test are removed with this revert.