server: case-sensitive duplicate locations on Windows break instruction init (core/instructions)

Summary

On Windows, opening the same folder with different drive/path letter casing creates two distinct loaded Locations (e.g. C:\dev\XRTemplate vs canonical C:\Dev\XRTemplate). Sessions created in the non-canonical-cased location consistently fail to start with Instruction initialization blocked by unavailable sources: core/instructions, while the canonical-cased location works.

Environment

• opencode version: v0.0.0-beta-19242
• OS: Microsoft Windows NT 10.0.26200.0 (Get-ComputerInfo: Windows 10 Pro, WindowsVersion 2009)
• Terminal: TERM=xterm-256color; TERM_PROGRAM/COLORTERM empty (original failure seen as a "Session failed" popup in the OpenCode client; reproduced headless via opencode2 api)
• Shell: ComSpec=C:\Windows\system32\cmd.exe (repro commands run via PowerShell)
• Install/channel: beta
• Active plugins: C:\Dev\opencode-fff-v2 (configured identically in both ~/.config/opencode/opencode.json and ~/.config/opencode/opencode.jsonc)

Reproduction

1. On Windows, have a project whose on-disk canonical path is C:\Dev\XRTemplate (dir C:\ shows Dev; git rev-parse --show-toplevel returns C:/Dev/XRTemplate; /api/project canonical is C:\Dev\XRTemplate).
2. Create a session with the non-canonical casing:
   opencode2 api post /api/session --data '{"location":{"directory":"C:\\dev\\XRTemplate"}}'
3. Send a message:
   opencode2 api post /api/session/<lowercase-session-id>/prompt --data '{"text":"ping"}'
4. Observe the session drain fail with Instructions.InitializationBlocked.
5. Repeat steps 2-3 with canonical C:\\Dev\\XRTemplate: instruction init succeeds and the run proceeds to the provider step (in my test it then failed only with a provider billing error, proving instructions loaded).

Expected Behavior

On a case-insensitive filesystem, C:\dev\XRTemplate and C:\Dev\XRTemplate should resolve to the same Location/project. Instruction discovery (AGENTS.md) should succeed regardless of the input casing.

Actual Behavior

Two separate locations stay loaded:

[{"directory":"C:\\dev\\XRTemplate"},{"directory":"C:\\Users\\small"},{"directory":"C:\\Dev\\XRTemplate"},{"directory":"C:\\dev"}]

The lowercase session fails on prompt with:

Instructions.InitializationBlocked: Instruction initialization blocked by unavailable sources: core/instructions
    at jE (B:/~BUN/root/chunk-w3nvgx7v.js:30:66822)
    at <anonymous> (B:/~BUN/root/chunk-w3nvgx7v.js:32:2899)
    at InstructionState.observe (B:/~BUN/root/chunk-w3nvgx7v.js:32:1283)
    ...
    at SessionRunner.drain (B:/~BUN/root/chunk-kva4f2k6.js:24:2279)

GET /api/session/<lowercase-id>/message returns {"data":[]} (blocked before any assistant step), while the uppercase session returns a normal assistant message. The client shows a "Session failed / Instruction initialization blocked by unavailable sources: core/instructions" popup.

Additional Context

• Frequency: consistent. Reproduced on demand 2026-09-07 on beta-19242. Historic /api/session list shows the same pattern: every location: C:\dev\XRTemplate (or c:\Dev\XRTemplate) session has outcome: failed with zero tokens, while C:\Dev\XRTemplate sessions succeed.
• Server log (~/.local/share/opencode/log/opencode.log, role=server) shows watcher subscribes/starts C:\Dev\XRTemplate\AGENTS.md for the canonical location, but no corresponding C:\dev\XRTemplate\AGENTS.md subscribe for the lowercase location — only global AGENTS.md entries. Lowercase boot still runs git rev-parse from C:\dev\XRTemplate but the subsequent remote get-url cwd flips to canonical C:\Dev\XRTemplate, suggesting the mismatch between Location string and git/project canonical path breaks discovery.
• Project listing confirms canonical: {"id":"2790c750067519a6185802abf291df9f47e482cc","canonical":"C:\\Dev\\XRTemplate","vcs":"git"}. A separate lowercase parent project C:\dev exists and works, so the breakage specifically hits the non-canonical project-subpath location.
• Config contents are valid (/api/config merges global opencode.json/opencode.jsonc plus project opencode.json with metavr/meta-xr-operator MCP and the fff plugin; only benign normalization warnings for legacy provider.qwen...reasoning and experimental.disable_paste_summary). Secrets redacted — not pasted.
• Workaround: opencode2 service restart, then only open C:\Dev\XRTemplate (canonical case). Avoid cd C:\dev\XRTemplate / lowercase recents.
• Test sessions created during diagnosis were deleted afterwards.