feat: Add ROI tracking with discovery_tokens for observations and session summaries (#111)

* feat: Add discovery_tokens for ROI tracking in observations and session summaries

- Introduced `discovery_tokens` column in `observations` and `session_summaries` tables to track token costs associated with discovering and creating each observation and summary.
- Updated relevant services and hooks to calculate and display ROI metrics based on discovery tokens.
- Enhanced context economics reporting to include savings from reusing previous observations.
- Implemented migration to ensure the new column is added to existing tables.
- Adjusted data models and sync processes to accommodate the new `discovery_tokens` field.

* refactor: streamline context hook by removing unused functions and updating terminology

- Removed the estimateTokens and getObservations helper functions as they were not utilized.
- Updated the legend and output messages to replace "discovery" with "work" for clarity.
- Changed the emoji representation for different observation types to better reflect their purpose.
- Enhanced output formatting for improved readability and understanding of token usage.

* Refactor user-message-hook and context-hook for improved clarity and functionality

- Updated user-message-hook.js to enhance error messaging and improve variable naming for clarity.
- Modified context-hook.ts to include a new column key section, improved context index instructions, and added emoji icons for observation types.
- Adjusted footer messages in context-hook.ts to emphasize token savings and access to past research.
- Changed user-message-hook.ts to update the feedback and support message for clarity.

* fix: Critical ROI tracking fixes from PR review

Addresses critical findings from PR #111 review:

1. **Fixed incorrect discovery token calculation** (src/services/worker/SDKAgent.ts)
   - Changed from passing cumulative total to per-response delta
   - Now correctly tracks token cost for each observation/summary
   - Captures token state before/after response processing
   - Prevents all observations getting inflated cumulative values

2. **Fixed schema version mismatch** (src/services/sqlite/SessionStore.ts)
   - Changed ensureDiscoveryTokensColumn() from version 11 to version 7
   - Now matches migration007 definition in migrations.ts
   - Ensures consistent version tracking across migration system

These fixes ensure ROI metrics accurately reflect token costs.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/services/sqlite/migrations.ts

@@ -471,6 +471,30 @@ export const migration006: Migration = {
   }
 };
 
+/**
+ * Migration 007 - Add discovery_tokens column for ROI metrics
+ * Tracks token cost of discovering/creating each observation and summary
+ */
+export const migration007: Migration = {
+  version: 7,
+  up: (db: Database) => {
+    // Add discovery_tokens to observations table
+    db.run(`ALTER TABLE observations ADD COLUMN discovery_tokens INTEGER DEFAULT 0`);
+
+    // Add discovery_tokens to session_summaries table
+    db.run(`ALTER TABLE session_summaries ADD COLUMN discovery_tokens INTEGER DEFAULT 0`);
+
+    console.log('✅ Added discovery_tokens columns for ROI tracking');
+  },
+
+  down: (db: Database) => {
+    // Note: SQLite doesn't support DROP COLUMN in all versions
+    // In production, would need to recreate tables without these columns
+    console.log('⚠️  Warning: SQLite ALTER TABLE DROP COLUMN not fully supported');
+    console.log('⚠️  To rollback, manually recreate the observations and session_summaries tables');
+  }
+};
+
 /**
  * All migrations in order
  */
@@ -480,5 +504,6 @@ export const migrations: Migration[] = [
   migration003,
   migration004,
   migration005,
-  migration006
+  migration006,
+  migration007
 ];