instructions: RangeError stack overflow activating AGENTS.md for case-variant Windows location #50750

Summary

On Windows, a location whose directory casing differs from its resolved project.directory (same project id, case-insensitive filesystem) makes instruction-source activation recurse infinitely: ancestorDirectories() never matches its stop argument (case-sensitive ===) and dirname("C:\") is a fixed point, so the walk overflows the stack (RangeError: Maximum call stack size exceeded) on every activation/reload. The failure handler then marks instructions unavailable, so that location silently receives no AGENTS.md instructions at all.

Environment

• opencode version: v2.0.14
• OS: Windows 10.0.22631.6199 (win32 x64)
• Terminal: TERM=xterm-256color (TERM_PROGRAM, COLORTERM unset)
• Shell: C:\WINDOWS\system32\cmd.exe (%ComSpec%); repro commands run in PowerShell 5.1
• Install/channel: global npm install of @opencode/cli, update channel latest
• Active plugins: ensure-claude-mem, gemini-env (global), claude-mem-opencode, graphify (project) — all active, all auto-discovered (no plugins key in any config). The crash happens in the built-in opencode.config.instruction source, unrelated to plugins.

Reproduction

1. On Windows (case-insensitive FS), have a project whose on-disk directory is C:\dev\krankly, and register a location that invoked the same directory with different casing (e.g., a client started from a historical cwd C:\dev\Krankly). Both locations share the same project id.
2. Confirm the mismatch:
   • GET /api/debug/location → [{"directory":"C:\\dev\\krankly"},{"directory":"C:\\dev\\Krankly"},{"directory":"C:\\Users\\<user>"}]
   • GET /api/location?location[directory]=C:\dev\Krankly → project.directory = "C:\\dev\\krankly" (case differs from directory)
3. Trigger instruction activation for the mismatched location: opencode api post /api/location/reload --param "location[directory]=C:\dev\Krankly" (it also fires on plugin/config reloads and watcher-driven rescans).
4. Read the server log.

Expected Behavior

The ancestor walk should treat start === stop the same way the branch gate does (case-insensitively on Windows, consistent with FSUtil.contains/path.relative), stop at the project root (or at the filesystem root as a safety net), and load that location's AGENTS.md instructions.

Actual Behavior

Every activation logs (4 occurrences in 3 minutes, one per reload cycle):

timestamp=2026-09-22T21:20:09.132Z level=WARN message="failed to activate instruction source" cause="Cause([Die(RangeError: Maximum call stack size exceeded.)])"
timestamp=2026-09-22T21:22:01.753Z level=WARN message="failed to activate instruction source" cause="Cause([Die(RangeError: Maximum call stack size exceeded.)])"
timestamp=2026-09-22T21:22:08.009Z level=WARN message="failed to activate instruction source" cause="Cause([Die(RangeError: Maximum call stack size exceeded.)])"
timestamp=2026-09-22T21:23:32.407Z level=WARN message="failed to activate instruction source" cause="Cause([Die(RangeError: Maximum call stack size exceeded.)])"

The catch then runs discovery.transform((editor) => editor.unavailable()): sessions under the C:\dev\Krankly location get no project AGENTS.md (verified — project rules were absent from that location's context while the identically-cased C:\dev\krankly location loaded them fine). The sibling warning failed to load instruction source never appears, confirming the crash happens before any source read (in the candidate-subscription walk, not in fs.up).

Additional Context

Root cause in the shipped file packages/core/src/config/plugin/instruction.ts (present at tag v2.0.14):

const project = discovery.project && FSUtil.contains(root, start)   // case-insensitive gate → true
const stop = FSUtil.contains(home, start) ? home : root             // root = "C:\dev\krankly"
// start = "C:\dev\Krankly"
const candidates = [...(project ? ancestorDirectories(start, stop) ... : [])]

function ancestorDirectories(start: string, stop: string): string[] {
  if (start === stop) return [start]                                 // case-sensitive → never true
  return [start, ...ancestorDirectories(dirname(start), stop)]       // dirname("C:\") === "C:\" → infinite recursion
}

• FSUtil.contains uses relative() (case-insensitive on win32), so the walk IS entered; start === stop compares raw strings and never matches C:\dev\Krankly vs C:\dev\krankly; walking up reaches C:\, where dirname("C:\") === "C:\" is a fixed point with no base case → stack overflow.
• Suggested fix: compare start/stop with the same case-folding used by contains (win32 case-insensitive), and/or add the parent === current base case that FSUtil.up/findUp/globUp already have:

function ancestorDirectories(start: string, stop: string): string[] {
  const eq = (a: string, b: string) => (process.platform === "win32" ? a.toLowerCase() === b.toLowerCase() : a === b)
  const out: string[] = []
  for (;;) {
    out.push(start)
    if (eq(start, stop)) return out
    const parent = dirname(start)
    if (parent === start) return out // filesystem root reached — stop instead of recursing
    start = parent
  }
}

• Note on current dev: packages/core/src/config/plugin/instruction.ts no longer exists (logic moved to packages/core/src/instruction-context.ts), which uses the iterative, root-guarded fs.up(). Two follow-ups: (1) confirm which releases up to v2.0.14 are affected and ship a fix/patch; (2) fs.up's options.stop === current comparison is still case-sensitive, so a case-differing start/stop walks all the way to the filesystem root instead of stopping at the project root (no crash, but it can pick up AGENTS.md files above the project).
• Frequency: consistent — fires on every activation/reload for the affected location.
• Workarounds: keep every client's cwd casing identical to the on-disk casing (prevents the mismatched location from being re-registered) and restart the service to drop in-memory locations. OPENCODE_DISABLE_PROJECT_CONFIG=1 skips the walk but disables project instructions everywhere.
• Recent changes: observed immediately after upgrading from v1.8.x to v2.0.14 (forced upgrade).