add TUI multi-session registry and focused-session root projection

[harryalbert]

Description

Adds TuiSessions, a process-local registry for retaining multiple live TUI terminal sessions and selecting which one is foreground. Each TuiSession owns a complete TuiTerminalSessionView plus the terminal manager that keeps its PTY and event loop alive. The eagerly-created view ID is also the session ID and shared-model terminal_surface_id, so the TUI does not introduce a second identity mapping.

RootTuiView becomes a projection of TuiSessions::focused_session() rather than the owner of one authenticated terminal child. Only the focused view is returned from child_view_ids() and rendered into the responder chain; background views remain alive without participating in layout or input routing. Login bootstrap creates and focuses the initial session through the same registry path that later orchestration children use.

Session activation restores the focused view's current input owner and exit-summary token. Subsequent PTY, blocker, CLI-subagent, and conversation-restore focus transitions are guarded by registry focus, preventing background sessions from stealing window focus or replacing the foreground resume hint.

This PR is the multi-session ownership primitive consumed by the local-child orchestration PR above. It intentionally does not add session navigation UI, persistence, or child-agent materialization.

Ownership and data flow

flowchart LR
  Bootstrap["Login bootstrap"] --> Create["Create full session view + terminal manager"]
  Create --> Registry["TuiSessions registry"]
  Registry --> Focused["Focused retained session"]
  Registry -. retains .-> Background["Background retained sessions"]
  Focused --> Root["RootTuiView projection"]
  Root --> Render["Render + responder chain"]
  Background -. excluded from .-> Render

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Linked Issue

CODE-1822 — Orchestration

Review guide

• crates/warp_tui/src/session_registry.rs — session identity, retained view/manager ownership, focused-session selection, activation, and events.
• crates/warp_tui/src/root_view.rs and crates/warp_tui/src/session.rs — focused-view projection and the unified login/session-creation path.
• crates/warp_tui/src/terminal_session_view.rs — focus-neutral construction, activation, background focus guards, and focused exit-summary ownership.
• specs/code-1822-tui-multi-session/TECH.md — as-built ownership model, non-goals, and validation contract.

Testing

• cargo check -p warp_tui --tests
• Added unit coverage for session registration/focus events and focused root projection with two retained full session views
  No user-facing changes yet

Agent Mode

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

CHANGELOG-NONE

Co-Authored-By: Oz oz-agent@warp.dev

[harryalbert]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• add product and tech spec #13855
• Add TUI orchestration tab bar specs #13832
• add reusable TUI tab bar component #13831
• rich message component #13777
• Add local child agents to TUI #13776
• add TUI multi-session registry and focused-session root projection #13775 👈 (View in Graphite)
• add TUI orchestration permission and configuration card #13717
• add reusable TUI option selector over shared option snapshots #13716 : 1 other dependent PR (#13830 )
• add reusable TUI editor view #13817
• route TUI editor input by owning-view focus #13771
• add option snapshots and adapt GUI orchestration pickers onto them #13714
• extract orchestration edit state into a frontend-neutral module #13707
• master

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[oz-for-oss]

@harryalbert

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[oz-for-oss]

Overview

This PR introduces a process-local TuiSessions registry, moves RootTuiView to project only the focused retained session, and updates TUI session focus/exit-summary handling so background sessions stay alive without participating in rendering or input routing.

Concerns

• No blocking correctness, security, or spec-drift concerns found in the annotated diff.
• The provided spec_context.md contains no approved or repository spec context, so there were no external spec commitments to compare beyond the PR's own checked-in TECH notes.

Verdict

Found: 0 critical, 0 important, 0 suggestions

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[kevinyang372]

As discussed offline, we should keep the Auth vs Terminal RootTuiState

[kevinyang372]

We should subscribe to explicit events

[kevinyang372]

Why do we need to retain and return a WindowId here? I don't think we really need that for TUI no?