cleanup: bump qwen2.5 → qwen3.5:latest in active defaults

stronger local rung is now the small-model-pipeline tier-1 default
across both Rust legacy + Go rewrite (cf. golangLAKEHOUSE phase 1).
same JSON-clean property as qwen2.5, more capacity. ollama still
serves both side-by-side; rollback is a 4-line revert if a workload
regresses.

active-default sites:
- lakehouse.toml [ai] gen_model + rerank_model → qwen3.5:latest
- mcp-server/observer.ts diagnose call (Phase 44 /v1/chat path) → qwen3.5:latest
- mcp-server/index.ts model roster doc → qwen3.5:latest first
- crates/vectord/src/rag.rs ContinuableOpts + RagResponse.model → qwen3.5:latest

skipped: execution_loop/mod.rs comments describing historic qwen2.5
tool_call quirks — those are documentation of past behavior, not
active defaults. data/_catalog/profiles/*.json are runtime-generated
(gitignored), not in scope for tracked changes.

cargo check -p vectord: clean. no behavioral change in the audit
pipeline — same JSON-clean local model, same think=Some(false)
posture, just stronger upstream.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lakehouse.toml

@@ -48,8 +48,13 @@ url = "http://localhost:3200"
 
 [ai]
 embed_model = "nomic-embed-text"
-gen_model = "qwen2.5"
-rerank_model = "qwen2.5"
+# Local-tier defaults bumped 2026-04-30: qwen3.5:latest is the
+# stronger local rung in the 5-loop substrate (per
+# project_small_model_pipeline_vision.md). Same JSON-clean property
+# as qwen2.5, more capacity. Ollama still serves both — bump back
+# in this file if a workload regressed.
+gen_model = "qwen3.5:latest"
+rerank_model = "qwen3.5:latest"
 
 [auth]
 enabled = false
@@ -72,7 +77,9 @@ min_recall = 0.9                          # never promote below this
 max_trials_per_hour = 20                  # hard budget cap
 
 # Model roster — available for profile hot-swap
+# qwen3.5:latest: stronger local rung — JSON-clean, 8K+ context,
+#                 default for gen_model and rerank_model
 # qwen3: 8.2B, 40K context, thinking+tools, best for reasoning tasks
-# qwen2.5: 7B, 8K context, fast, good for SQL generation
-# mistral: 7B, 8K context, good for general generation
+# qwen2.5: 7B, 8K context, fast — kept loaded for the 2026-04 era
+#          comparison runs; new defaults use qwen3.5:latest
 # nomic-embed-text: 137M, embedding-only, used by all profiles