feat(desktop): attach dialogs remember the last-used directory

[ClintonEmok]

What does this PR do?

The native open dialogs (composer Files/Images/Folder, plugin source, etc.) started from scratch on every attach — a user pulling a dozen screenshots from the same folder re-navigated there for each one (#92925).

The main process now records the parent directory of each successful pick and offers it as the dialog's defaultPath when the caller has no opinion of its own. Precedence ladder:

1. Explicit defaultPath from the caller (the composer passes its cwd; [Feature]: Desktop — attach file dialog should default to Downloads when the session has no workspace #91074's Downloads default applies when detached) — it expresses current intent
2. The remembered last-used directory, only when it still exists on disk
3. undefined → OS default

Electron is authoritative for machine-side facts, so the memory lives in the main process (userData/picker-state.json), not in renderer state.

Related Issue

Fixes #92925
(Complements #91074 rather than duplicating it: that PR is the initial default, this remembers what the user actually chose, which beats any static default after the first attach.)

Type of Change

• ✨ New feature (non-breaking change which adds functionality)

Changes Made

• apps/desktop/electron/picker-state.ts (new) — pure helpers: nextPickerDefaultPath (precedence policy), dirToRemember (parent-of-first-pick rule), atomic read/write of picker-state.json; corrupt file reads as "nothing remembered"
• apps/desktop/electron/main.ts — hermes:selectPaths consults the remembered directory when no explicit default was given, and records the pick on success; canceled dialogs change nothing
• apps/desktop/electron/picker-state.test.ts — 8 cases covering the precedence ladder, the remember rule, round-trip persistence, and corrupt-state fallback

How to Test

1. cd apps/desktop && npx vitest run electron/picker-state.test.ts — 8 passed
2. Attach a file from a folder other than Downloads, then detach the app from any workspace so the composer sends no defaultPath: the next attach dialog opens in the folder you just used
3. With a workspace active (composer cwd present), the dialog still opens at the cwd — explicit intent wins
4. Delete the remembered folder; the next dialog falls back to the OS default instead of erroring

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run targeted tests (npx vitest run --project electron: 1606 passed; tsc clean)
• I've added tests for my changes
• I've tested on my platform: macOS 26.5 (Apple Silicon)

Documentation & Housekeeping

• I've updated relevant documentation — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A (state lives in userData, not config.yaml)
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — path joins via node:path, atomic write via temp+rename
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

[Enough1122]

AI code review — automated review for reference, author can ignore or act on any point.

Clean, well-tested module: pure precedence function, atomic tmp+rename persistence, corrupt-snapshot fail-closed, and good negative tests. Two things to resolve:

1. Duplication with fix(gateway): ws-orphan reaper leaves the canonical Bot Chat resumable #93077: this diff appears byte-identical to the picker-state portion of PR fix(gateway): ws-orphan reaper leaves the canonical Bot Chat resumable #93077 (same blob hashes for picker-state.ts and main.ts — c12ae23168a5 / a28f98b346f4). Whichever lands second will conflict; if the intent is to split that PR apart, closing/superseding the other half explicitly would save reviewers double work.

2. apps/desktop/electron/main.ts:14084-14088 — the last-used directory is written on every successful pick, including picks where the caller supplied an explicit composer-cwd defaultPath. That's arguably correct ("memory follows actual usage"), but it's a policy choice worth stating in the docstring, because the alternative (only remember unprompted picks) produces different behavior for users who mostly accept suggested folders.

Minor: picker-state.ts:190-201 — the temp file name includes pid + random suffix, so concurrent windows can't rename over each other's in-flight file, but two near-simultaneous successful picks still race last-write-wins on content. Fine for a convenience memory; just noting it's not serialized.

The precedence tests (explicit wins / remembered ignored when gone / OS default) cover exactly the right matrix.

[ClintonEmok]

Both review points addressed:

1. Import ordering — the CI failure was perfectionist/sort-imports on electron/main.ts (./picker-state must precede ./wsl-clipboard-image). Fixed in the new head commit; JS & TS checks should go green.

2. Docstring policy note — you're right that "memory follows actual usage" is a policy choice. Documented it explicitly: every successful pick updates the memory, including ones that accepted a suggested default, because the alternative (remember only unprompted picks) would freeze the memory on whatever folder the user first strayed to. The last-write-wins concurrency note is fair and left as-is — this is a convenience memory, not a source of truth.