feat: Register SDK hooks for tool monitoring and error handling

[PureWeen]

Problem

PolyPilot registers zero SDK hooks despite 6 being available (PreToolUse, PostToolUse, UserPromptSubmitted, SessionStart, SessionEnd, ErrorOccurred). Instead, tool monitoring is done by counting ToolExecutionStartEvent/ToolExecutionCompleteEvent events, and error handling is scattered across multiple catch blocks.

SDK Hooks Available

Hook	Input	Key Outputs	Potential Use
OnPreToolUse	ToolName, ToolArgs, Cwd	PermissionDecision (approve/deny), ModifiedArgs, AdditionalContext	Accurate tool call tracking, per-worker tool restrictions, inject context before tools
OnPostToolUse	ToolName, ToolArgs, ToolResult	ModifiedResult, AdditionalContext, SuppressOutput	Post-process tool results, accurate completion tracking
OnUserPromptSubmitted	Prompt, Cwd	ModifiedPrompt, AdditionalContext	Prompt rewriting, context injection
OnSessionStart	Cwd, Source, InitialPrompt	AdditionalContext, ModifiedConfig	Custom initialization
OnSessionEnd	Reason, FinalMessage, Error	CleanupActions, SessionSummary	Custom cleanup, session summaries
OnErrorOccurred	Error, ErrorContext, Recoverable	ErrorHandling, RetryCount, UserNotification	Centralized error recovery instead of scattered try/catch

JS-Only Hooks (not in .NET SDK yet):

• AgentStop — fires when agent stops; can return decision: "block" to force continuation
• SubagentStop — same for subagents; could prevent workers from stopping too early

What to Change

Phase 1 (low risk):

1. Register OnPreToolUse and OnPostToolUse for accurate tool call counting — replace ActiveToolCallCount event-based tracking
2. Register OnErrorOccurred for centralized error handling with retry support

Phase 2 (medium risk):

3. Use OnPreToolUse with SessionConfig.AvailableTools/ExcludedTools to enforce tool restrictions per worker role
4. Use OnUserPromptSubmitted to inject dynamic context (e.g., squad decisions.md) at prompt time instead of in BuildWorkerPrompt

Phase 3 (when .NET SDK adds them):

5. Use AgentStop/SubagentStop to supplement watchdog — could reduce some timeout tiers

Note

Hooks supplement but do NOT replace the custom watchdog (see processing-state-safety skill SDK migration matrix for why).

[PureWeen]

Update: SDK v0.2.2 available

The hooks API (OnPreToolUse, OnPostToolUse, OnErrorOccurred, OnSessionStart, OnSessionEnd) remains available and unchanged in v0.2.2. These could supplement our watchdog's ActiveToolCallCount tracking, especially for the live-event-stream gap (PR #619) where ToolExecutionStartEvent isn't delivered via the live stream.

Specific opportunity: OnPreToolUse/OnPostToolUse hooks fire synchronously in the SDK pipeline, potentially more reliable than the live event stream. If adopted, they could:

• Reliably increment/decrement ActiveToolCallCount without the live-stream gap
• Reduce dependence on events.jsonl freshness checks and GetLastEventType fallbacks
• Simplify the TurnEnd fallback guard logic

Still requires design review — hooks run on SDK threads, need UI thread marshaling.