TUI "edit task" silently resets session ID, pin, permission mode, tags, and other persisted fields

[kylecarbonneau]

Summary

Editing a task through the TUI (e on a selected task) and saving resets several
persisted columns to their zero value, even when the user only changed the title or body.
The edit form models a subset of fields; everything it doesn't model — and that the
save-reconciliation doesn't explicitly re-apply — is overwritten with empty/zero on
UpdateTask.

Affected fields

On every TUI edit-save, these are silently reset:

• claude_session_id → "" — breaks conversation resume for the task
• daemon_session → "" — loses the tmux daemon-session association
• port → 0
• pr_info_json → "" — cached PR/CI state dropped (PR URL/number survive)
• permission_mode → "" and dangerous_mode → false — silently reverts the task
  to prompt mode, even if it was set to auto/dangerous
• pinned → false — silently unpins a pinned task
• tags → "" — tags lost
• source_branch → ""

Fields the form does preserve (so they're safe): title, body, status, type, project,
executor, effort level, PR URL/number, worktree path, branch name, timestamps.

Root cause

internal/ui/form.go::NewEditFormModel reads only Title, Body, Type, Project, Executor,
EffortLevel, PRURL, PRNumber from the task. On save,
internal/ui/app.go::updateEditTaskForm calls FormModel.GetDBTask() (which rebuilds a
fresh Task from just those form fields) and then re-applies only a hand-picked subset
(ID, Status, WorktreePath, BranchName, CreatedAt, StartedAt, CompletedAt). It then calls
db.UpdateTask, whose UPDATE tasks SET ... writes a fixed column set — so any column it
writes that was neither in the form nor re-applied gets the zero value.

The same shape affects the project-move paths
(internal/ui/app.go::moveTaskToProject, cmd/task/main.go::moveTask), which rebuild the
task and only copy a subset of fields.

Reproduction

1. Create a task; pin it (p) and set it to auto/dangerous permission mode.
2. Let it run so it has a claude_session_id.
3. Select it, press e, change only the title, save.
4. Observe: the task is unpinned, permission mode is back to prompt, and resuming the
   conversation no longer finds the prior session.

Suggested fix

Two reasonable directions:

• Targeted: in updateEditTaskForm's reconciliation block, carry through every
  persisted field the edit form doesn't expose (mirror how Status/WorktreePath are
  preserved) — i.e. start from the original task and overlay only the form-edited fields,
  rather than starting from a blank GetDBTask() result.
• Structural (preferred): have the edit form load and round-trip the full task, or
  give UpdateTask a field-mask / partial-update variant so callers only write the
  columns they actually intend to change.