fix: prevent stack overflow in earlyResolve() on circular dependencies

[claude-do]

Summary

Fixes a stack overflow (RangeError: Maximum call stack size exceeded) in ConfigItem.earlyResolve() when the @currentEnv env flag item or @import enabled dependencies have circular references.

• earlyResolve() runs during finishInit() — before finishLoad() where findGraphCycles() provides cycle detection — so circular dependencies cause unbounded recursion and a process crash
• Added isResolved idempotency guard (matching the existing guard in resolve()) to prevent redundant re-resolution on diamond dependencies
• Added Set<string>-based cycle detection parameter, following the same recursionStack DFS pattern already used in findGraphCycles() (graph-utils.ts)
• Wrapped the DirectoryDataSource._finishInit() call site in try/catch so cycle errors surface as _loadingError instead of uncaught exceptions

Changes

File	Change
packages/varlock/src/env-graph/lib/config-item.ts	Add isResolved guard + cycle detection via optional resolving Set param; fix typos
packages/varlock/src/env-graph/lib/data-source.ts	Wrap earlyResolve() at line 704 in try/catch
packages/varlock/src/env-graph/test/environments.test.ts	Add 3 tests: self-referencing cycle, indirect cycle, diamond dependency (no cycle)

Test plan

• All 255 existing tests pass (bunx vitest --run)
• New test: self-referencing env flag (APP_ENV=$APP_ENV) produces loading error, not crash
• New test: indirect cycle via env flag (APP_ENV=$OTHER, OTHER=$APP_ENV) produces loading error
• New test: diamond dependency (no cycle) in env flag resolves correctly
• Lint clean (bun run lint:fix)

🤖 Generated with Claude Code

[claude-do]

Real-world reproduction & verification

Reproduced this bug in a real project (goalserve-poc demo-pwa) and confirmed the fix resolves it.

Root cause

The project's .env.schema contains:

# @currentEnv=$APP_ENV
APP_ENV=fallback($APP_ENV, $VARLOCK_ENV, "development")

APP_ENV references itself via fallback($APP_ENV, ...), creating a self-referencing cycle that earlyResolve() follows infinitely — exhausting the heap before findGraphCycles() ever runs.

Before the fix

varlock load crashes with OOM regardless of memory cap:

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
Aborted

• With 512MB cap: OOM after ~8s (trace 1)
• With 256MB cap: OOM after ~4s (trace 2)

After the fix

Clean, immediate error:

🚨 Error encountered while loading directory - /home/claude/code/goalserve-poc/apps/demo-pwa

Circular dependency detected during early resolution: APP_ENV

(post-fix trace)

Environment

• Node v22.22.1
• varlock 0.4.1
• Linux x86_64, 8GB RAM

Full environment details in varlock-env-info.log.

The fix was also verified by patching the compiled chunk-PCRIVT4T.js directly in node_modules — both the earlyResolve() cycle detection and the _finishInit() try/catch behaved correctly.