[guyskk]

Summary

Replace the hard guard (refuse-to-start) approach with automatic override via Claude Code's --settings CLI parameter.

Key Discovery

--settings has "Command line arguments" priority (level 2), which is higher than User settings (level 5, ~/.claude/settings.json). The env from --settings merges with settings.json env, with same-name keys overridden by --settings, different keys preserved.

Empirical proof: docs/discuss-20260609-env-override.md

Changes

• Remove checkSettingsEnvConflict() and checkValidateEnvConflict()
• Remove FilterUserEnvForSettings(), DetectSettingsEnvConflicts(), FormatEnvConflictError() and env_guard.go
• Add buildProviderSettingsJSON() to serialize provider env as --settings JSON with env var expansion
• SwitchWithHook() now preserves user's complete env in settings.json
• runClaude() passes provider env via --settings parameter

Behavior Change

Before	After
settings.json env conflict → error and abort	settings.json env conflict → --settings auto-override
settings.json conflicting keys filtered/deleted	settings.json preserves user's complete env
User must manually clean settings.json	User needs no action

Verification (7 scenarios, real claude 2.1.169 process)

1. Conflict override: settings.json ANTHROPIC_BASE_URL overridden by --settings ✅
2. Non-conflict preserve: settings.json CCC_TEST_CLAUDE_VAR preserved ✅
3. ANTHROPIC_MODEL preserve: settings.json ANTHROPIC_MODEL preserved when provider has no such key ✅
4. Mixed conflict+non-conflict: conflict key overridden, non-conflict key preserved ✅
5. Multiple CLAUDE_/ANTHROPIC_ preserve: all preserved when provider has no such keys ✅
6. Process env preserve: process env ANTHROPIC_* keys preserved ✅
7. Full chain (simulated ccc): provider env overrides conflict keys, non-conflict keys preserved ✅

Testing

• All 133 tests pass
• Lint, test, build all pass via ./check.sh
• New tests for buildProviderSettingsJSON() (nil, empty, single key, multiple keys, special chars, env var expansion)