Introduce cut/copy/paste support - #18

* Only terminate thread if it did not already end

* Remove debug client when its terminated

zed-industries#18)

…ask zed-industries#18)

Replaces the inline-base64 image flow with proper chunked upload.
Wire is binary WebSocket frames (no JSON, no base64). 16-byte header
(u64 upload_id + u64 offset, BE) prefixes each chunk's raw bytes.
Server buffers chunks in tmp files keyed by server-generated u64 id;
1h TTL GC. send_message_blocks resolves spk-upload://<id> ResourceLinks
into acp::ContentBlock::Image just before forwarding to ACP, so the
agent sees the same Image block as today. Mobile starts upload the
moment a file is picked; UI shows per-attachment progress; Send is
gated until all uploads complete. Reconnect resume via upload_status;
force-kill resume via per-server EncryptedSharedPreferences. WS cap
dials back from 32 MiB (zed-industries#15 hotfix) to 1 MiB once chunked lands.

- plan doc ticked for zed-industries#18 (chunked upload) + final 6 commit SHAs appended
- INDEX.md: 3 new rows (chunked upload, cold-session wake, morning fixes)
- one note added re. inverted dep direction (BinaryFrameHandler indirection
  vs original sketch's solution_agent dep, which would have feature-unified
  a second rustls CryptoProvider and broken the TLS handshake)

Archive phases 13 (toolbar/gutter), 14 (save-conflict + reload), 15 (counter
reset + clear outputs), and 16 (DataFrame tables) — all user-confirmed
2026-07-11.

Plan the next phases from testing feedback:
- Phase 17: execution status & queue correctness (pending vs running, per-cell
  timing that no longer inherits a long cell's wait, Run All status/tick reset,
  restart/interrupt cancellation, shift-enter-no-kernel skip).
- Phase 18: move execution status/time into the cell (VS Code style) + finish
  centering the gutter run button.
- Phase 19: configurable post-run landing mode (command/edit/remember).

File bugs zed-industries#18 (executing doesn't mark dirty, so external save auto-reloads and
discards runs) and zed-industries#19 (reload doesn't clear the conflict toast). Add backlog
items for multi-select cells, a live elapsed-time counter, and further table
polish.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014eseBDGa7au9r2VxBHeh9X

An executed-but-unedited notebook reported itself clean, so an external save
silently auto-reloaded and discarded the run results (outputs + execution
counts), even though that state differs from disk and is savable.

Track it with an execution_state_changed flag OR'd into Item::is_dirty. The
flag is set when a run is submitted or queued, when kernel output/count
messages are routed to a cell, on clear-cell/all-outputs, and on the restart
counter reset; it clears on save (mark_as_saved) and on reload. External
changes now surface the conflict toast instead of silently reloading over an
executed notebook, and the tab dirty indicator reflects execution state.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014eseBDGa7au9r2VxBHeh9X

 follow-through)

Two defects found in self-review of the bug zed-industries#18 fix, both in the
save-while-a-cell-is-running scenario:

- The dirty flag was set for EVERY kernel message routed to a cell, including
  Status busy/idle broadcasts that change no savable content, so a save
  during a run was immediately re-dirtied for no reason. Only content-bearing
  messages (stream/display data/result/input/error) set it now.

- After our own save, an output arriving before the file watcher delivered
  the Reloaded event made the notebook look dirty again, so
  handle_external_change treated our own write as an external conflict and
  raised the toast. A new last_saved_disk_text field records exactly what we
  last wrote (or loaded/reloaded), and the external-change handler recognizes
  our own save by comparing against it before the dirty check. Recorded on
  open, save, save_as, reload, and external auto-reload.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014eseBDGa7au9r2VxBHeh9X

Introduce cut/copy/paste support