[BUG] VSCode extension: `/resume` empty when workspace is on a UNC network path (sessions-index.json overwritten with truncated set)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When the VSCode workspace is opened from a UNC network path (e.g. \\host\share), the Claude Code extension writes sessions-index.json with only ~3 entries (current + 2 recent sessions), actively overwriting any larger index on disk within seconds. As a result, /resume and the "Past Conversations" dropdown are effectively empty even when dozens of valid .jsonl session files exist.

In the project dir under ~/.claude/projects/<UNC-project-hash>/:

$ ls *.jsonl | wc -l
40

$ python -c "import json; print(len(json.load(open('sessions-index.json'))))"
3

/resume lists only the 3 indexed sessions. The other 37 .jsonl files are valid and loadable — claude --resume <id> from the CLI works for any of them.

The same VSCode + same extension version works correctly when the workspace is a local path. Downgrading the extension to 2.0.56 does not fix it. The bug is isolated to the VSCode extension's index-write path when the workspace is UNC.

What Should Happen?

/resume and the "Past Conversations" dropdown should list all sessions stored as .jsonl files in the project dir, regardless of whether the VSCode workspace is on a local or UNC path. The extension should not truncate sessions-index.json to ~3 entries when the workspace is UNC.

Error Messages/Logs

Steps to Reproduce

1. Open a UNC-path folder in VSCode (e.g. \\server\share).
2. Start the Claude Code extension; have a conversation.
3. In a terminal, manually rebuild sessions-index.json from the .jsonl files in ~/.claude/projects/<hash>/ (40 entries written).
4. Re-check the entry count within ~5 seconds — it's back to 3. No VSCode restart needed; the extension rewrites the index while running.
5. Repeat steps 1–4 with a local-path workspace (e.g. C:\some\folder) — /resume lists all sessions correctly and the index is not truncated.

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Code VSCode extension: 2.1.114 (also reproduced on 2.0.56 after downgrade — version is not the trigger)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Environment

• Claude Code VSCode extension: 2.1.114 (also reproduced on 2.0.56 after downgrade — version is not the trigger)
• VSCode: latest stable
• OS: Windows 11 Pro 26200
• Workspace: UNC path \\<host>\<share> (Samba share)

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Additional context / related issues

Different failure modes of the same file: #25032, #24729, #22878, #44346, #39667, #41616, #12908. None of those mention UNC-path triggering, which is the distinguishing detail here.