fix(coordinator): clear focus_target on cancel regardless of phase

[appergb]

User description

Summary

`finish_cancel_session_state` only cleared `state.focus_target` when the cancelled phase was not `Processing`. A Processing-phase cancel therefore left the stale window-resource handle in place until the next `begin_session_state` overwrote it. Between cancel and the next `begin_session`, any reader of `focus_target` sees a value belonging to a session that is about to be torn down.

Why this matters

Today the leak is bounded — `begin_session_state` always overwrites `focus_target` (`coordinator_state.rs:80`), and there is no documented reader that races with that interval. So this isn't user-visible today. But the asymmetry is a footgun: anyone wiring a new code path that consults `focus_target` between cancel and next session would silently inherit the stale handle.

Change

Move `state.focus_target = None` ahead of the phase check so it always fires when the cancel was accepted (i.e. not rejected for `Idle` / `Inserting` phases). Phase transition stays conditional on the original non-Processing branch — `end_session` must still own the `Processing → Idle` collapse to avoid racing with the polish/insert tail of `Processing`.

Audit linkage

Audit ID 3.3.5 (CONFIRMED). See `docs/audit-2026-05-10-validated.md` (local) for full validation context.

Test plan

• `cargo test --manifest-path openless-all/app/src-tauri/Cargo.toml --lib coordinator_state` — 9/9 passing.
• Tightened `cancel_session_state_machine_is_table_driven` to assert `focus_target` clears for every accepted phase (including Processing) and stays untouched on rejected cancels (Idle / Inserting). Test fails on the old code (regression-guard).
• CI build — to be verified

Pure state-machine bookkeeping fix; no runtime behavior change in any documented path. Awaiting manual verification of cancel-during-polish on a real build.

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PR Type

Bug fix, Tests

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Description

• Move focus_target clearing before phase check

• Retain conditional phase transition for Processing

• Assert focus_target cleared after accepted cancels

• Assert focus_target unchanged after rejected cancels

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Diagram Walkthrough

flowchart LR
  A["begin_cancel_session_state"] --> B{"Phase accepted?"}
  B -- "No (Idle/Inserting)" --> C["Return None"]
  B -- "Yes" --> D["finish_cancel_session_state"]
  D --> E["Clear focus_target"]
  E --> F{"Phase != Processing?"}
  F -- "Yes" --> G["Set phase to Idle"]
  F -- "No" --> H["Leave phase for end_session"]

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File Walkthrough

Relevant files

Bug fix

coordinator_state.rs Clear focus_target on cancel in all phases                              openless-all/app/src-tauri/src/coordinator_state.rs Move state.focus_target = None before the phase check so it clears on every accepted cancel (including Processing) Update doc comment to explain why focus_target must always be released, referencing audit 3.3.5 Enhance cancel_session_state_machine_is_table_driven test to assert focus_target is None after any accepted cancel and remains untouched on rejected cancels +18/-4

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[github-actions]

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