feat: Add Claude Code CLI flag passthrough for delegation

[kaitranntt]

Problem

CCS delegation system (built Nov 2025) uses basic claude -p with stream-json output. Claude Code has evolved significantly with new CLI capabilities that ccs doesn't leverage, potentially missing cost controls, reliability features, and modern subagent integration.

Current Gap Analysis

Claude Code now supports these flags that CCS doesn't pass through:

Flag	Purpose	Value for CCS
--max-budget-usd	Cost limit per session	Prevent runaway delegation costs
--max-turns	Limit agentic turns	Prevent infinite loops
--fallback-model	Auto-fallback on overload	Reliability when model unavailable
--agents	Dynamic subagent JSON	Inject ccs profiles as native subagents
--json-schema	Structured output validation	Parseable delegation results
--tools	Restrict available tools	Security/scope control

Key Findings

1. CLI Reference (Dec 2025): Claude Code supports --agents flag for dynamic subagent injection at runtime - could bridge ccs profiles into native subagent system.

2. Headless Mode: Full --output-format stream-json works well. Missing --max-budget-usd for cost guardrails.

3. Current Implementation: HeadlessExecutor already has extraArgs passthrough mechanism, but no explicit support for new flags.

Proposed Solution

Add passthrough support for key Claude Code CLI flags to HeadlessExecutor and DelegationHandler:

# New supported flags
ccs glm -p "task" --max-budget-usd 1.00     # Cost limit
ccs glm -p "task" --max-turns 5              # Turn limit
ccs glm -p "task" --fallback-model sonnet    # Overload fallback

Files to Modify

• src/delegation/headless-executor.ts - Add flag passthrough logic
• src/delegation/delegation-handler.ts - Expose options in CLI parsing
• src/commands/help-command.ts - Update --help output

Acceptance Criteria

• --max-budget-usd flag passthrough works
• --max-turns flag passthrough works
• --fallback-model flag passthrough works
• Flags appear in ccs --help output
• TypeScript strict mode passes
• All existing tests continue to pass