perf: Cache size of 3 graphs causes thrashing on SWE-BENCH

[greynewell]

Problem

The cache in src/cache/graph-cache.ts:294 only holds 3 graphs:

this.maxGraphs = options?.maxGraphs || 3;  // Only 3 graphs!

SWE-BENCH agents typically analyze multiple directories or switch between subsystems, causing constant cache eviction.

Example Failure Scenario

1. Analyze django/core          → Cache: [core]
2. Analyze django/contrib       → Cache: [core, contrib]  
3. Analyze django/db            → Cache: [core, contrib, db]
4. Back to django/core (edit)   → Cache: [contrib, db, core] (evicted!)
5. Check django/contrib again   → CACHE MISS! Re-fetch everything

Impact on SWE-BENCH

• 30-50% increased latency from cache misses
• Repeated API calls and re-zipping
• Higher costs
• Agents may abandon tool due to slowness

Proposed Fix

this.maxGraphs = options?.maxGraphs || 20;  // At least 20
this.maxNodes = options?.maxNodes || 1000000;  // 1M nodes

Most SWE-BENCH repos have 10k-50k nodes, so 20 graphs = plenty of headroom.

Priority

🟠 HIGH - Significant performance impact on benchmark