Fix remote-control session end removing local input box (APP-4604)

[vorporeal]

Description

Fixes APP-4604: after a /remote-control session with a local orchestrator hit the 100MB session-sharing limit, the local Warp app rendered the conversation as completed and removed the input box, blocking further input.

The 100MB error itself is expected — it's the per-session max_session_bytes_size sharing limit enforced client-side, which terminates the shared session. The bug is in how the client reacts to the session ending.

QUALITY-726 (#11465) changed /remote-control to start a User share that carries a sidecar orchestrator source_task_id. TerminalModel::ambient_agent_task_id() now returns that id, so when the shared session ends, on_session_share_ended runs the cloud-handoff continuation logic (cloud_conversation_continuation_ui_state) and can insert a "conversation ended" tombstone — removing the input box — even though the local conversation is still running. The same path also triggers on a normal stop of remote control, not just the 100MB error.

This change gates the continuation logic so it only applies to genuine cloud (ambient agent) conversations: it bails out when the session source is set to a non-ambient (User) kind. Sessions with no source (e.g. restored cloud-mode panes, finished viewers) are unaffected, preserving the cloud-handoff and restored-tombstone flows. This matches QUALITY-726's stated invariant that a User share carrying source_task_id must not activate cloud UI.

Linked Issue

APP-4604 (Linear)

Testing

• Added regression test test_on_session_share_ended_keeps_input_for_user_share_with_source_task_id covering a User share with a source_task_id whose task would otherwise resolve to a tombstone — asserting no tombstone is inserted and the input box stays editable.

• Ran the shared-session continuation/tombstone test suite (11 tests) — all pass, including existing cloud-handoff, finished-viewer, and restored-tombstone cases.

• cargo fmt (no changes) and cargo clippy -p warp --lib --tests -- -D warnings (clean).

• I have manually tested my changes locally with ./script/run

Agent Mode

• Warp Agent Mode - This PR was created via Warp's AI Agent Mode

Conversation: https://staging.warp.dev/conversation/08db43ce-12cb-42f7-ae6a-cda89706c3da
Run: https://oz.staging.warp.dev/runs/019e6012-9dfa-79e0-a2df-ba140bd4ab2a

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Overview

This PR gates cloud handoff continuation handling so non-ambient /remote-control user shares with a sidecar source_task_id do not render the conversation-ended tombstone, and it adds a regression test for that path.

Concerns

• ⚠️ [IMPORTANT] For this user-facing change, please include screenshots or a screen recording demonstrating the remote-control session-end path keeping the local input box available end to end.

Verdict

Found: 0 critical, 1 important, 0 suggestions

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