fix: file explorer not switching workdir on session change

[saucam]

Summary

Three bugs in the file-tree state when switching sessions in the web UI:

1. resetFileTreeForSession was a no-op (SolidJS merge bug)
setState("bySession", id, {}) uses SolidJS's path-setter with a plain-object argument, which performs a merge (not a replace). Since the merged object is empty, the old session's entries were never cleared — memory wasn't reclaimed and the old session's tree state persisted indefinitely.

Fixed by using produce() (immer-style assignment) to do an actual replacement.

2. Stale entries shown without a loading indicator on session switch
loadDirectory sets loading: true but does not clear existing entries. The loading indicator condition is loading && entries === null, so if stale entries existed (from a previous visit), no spinner appeared. The user saw the old session's file listing while the new fetch was in-flight.

Fixed by adding a clearFirst?: boolean option to loadDirectory. When clearFirst: true, entries are cleared before the request so the loading… spinner always appears. Used in the FileTree effect on every session switch.

3. No workdir path shown in the FileTree header
The header displayed "Files" without indicating which session's working directory was shown. Users couldn't confirm the tree had switched sessions.

Fixed by adding the current session's workdir below the header (truncated with full path on hover).

Test plan

• web/src/state/files.test.ts (9 new tests): loadDirectory with/without clearFirst, resetFileTreeForSession clears state
• Full web test suite: 104 tests pass
• Daemon test suite: 504 tests pass
• TypeScript type check: no errors
• ESLint: no errors

Closes #36

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • The file tree now shows the current working directory in the sidebar when a session is selected.
  • Switching sessions now refreshes the root folder with a clearer loading state.

• Bug Fixes

  • File tree contents no longer linger briefly from a previous session while new data is loading.
  • Session changes now reset file tree state more reliably, improving consistency across views.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 782ab61c-8a4e-4139-a006-5b9f0bff3bb3

📥 Commits

Reviewing files that changed from the base of the PR and between 5bc05ec and f83f0b5.

📒 Files selected for processing (3)

• web/src/components/files/FileTree.tsx
• web/src/state/files.test.ts
• web/src/state/files.ts

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📝 Walkthrough

Walkthrough

The file tree now reloads the focused session root with explicit clearing, shows the active workdir in the header, and the file-tree store and tests support the new clear-first loading and reset behavior.

Changes

File tree session refresh

Layer / File(s)	Summary
Store loading and reset behavior web/src/state/files.ts	loadDirectory now accepts clearFirst, clears entries and expanded before reload, and session reset replaces the per-session node map.
Session switch UI web/src/components/files/FileTree.tsx	The focused-session effect reloads the root directory with clearFirst: true, and the header renders workdir in a truncated monospace line.
State tests web/src/state/files.test.ts	Vitest coverage exercises stale-entry clearing, successful reloads, session isolation, and session reset behavior.

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the session-switch/workdir bug fixed by the PR.
Linked Issues check	✅ Passed	The changes implement the linked session-switch fix: clear-first loading, workdir header, and state reset cleanup.
Out of Scope Changes check	✅ Passed	The edits stay within the file-explorer/session-switch fix and its tests, with no unrelated feature work.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/file-explorer-session-switch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.69%. Comparing base (5bc05ec) to head (f83f0b5).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #37   +/-   ##
=======================================
  Coverage   59.69%   59.69%           
=======================================
  Files          47       47           
  Lines        7255     7255           
=======================================
  Hits         4331     4331           
  Misses       2924     2924           

Flag	Coverage Δ
daemon	59.69% <ø> (ø)

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