.archon: add lakehouse-architect-review workflow

Demonstrates Archon → Pi → our gateway → OpenRouter end-to-end on
Lakehouse code. Three Pi nodes (shape, weakness, improvement) — each
fires a /v1/chat/completions call that lands a Langfuse trace AND an
observer event for KB-consolidation parity with scrum.

Run:
  ARCHON_SUPPRESS_NESTED_CLAUDE_WARNING=1 \
  PI_OPENROUTER_BASE_URL=http://localhost:3100/v1 \
  OPENROUTER_API_KEY=sk-anything \
  archon workflow run lakehouse-architect-review --no-worktree

Verified 2026-04-26 — 3 grok-4.1-fast calls, 14.6s total, observer ring
delta=3, three Langfuse traces. Read-only (allowed_tools: [read]) so
running it doesn't mutate the repo.

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

.archon/workflows/lakehouse-architect-review.yaml

@@ -0,0 +1,42 @@
+# Real Archon workflow on the Lakehouse repo, fully via our gateway.
+# Three Pi nodes, each fires LLM → /v1/chat/completions → OpenRouter,
+# every call lands a Langfuse trace + observer event.
+#
+# Read-only (allowed_tools: [read]). Don't pass --branch / leave
+# --no-worktree at runtime so Archon doesn't try to create a worktree.
+name: lakehouse-architect-review
+description: 'Pi reviews Lakehouse architecture in 3 turns through our gateway.'
+provider: pi
+model: openrouter/x-ai/grok-4.1-fast
+
+nodes:
+  - id: shape
+    prompt: |
+      Read these files and answer in 3 short bullets describing the
+      architectural shape of Lakehouse:
+      - /home/profit/lakehouse/Cargo.toml
+      - /home/profit/lakehouse/lakehouse.toml
+      - /home/profit/lakehouse/docs/MODE_RUNNER_TUNING_PLAN.md
+      Be terse. No preamble.
+    allowed_tools: ["read"]
+    effort: low
+    idle_timeout: 90000
+
+  - id: weakness
+    prompt: |
+      Read /home/profit/lakehouse/crates/gateway/src/v1/mod.rs and
+      identify ONE real weakness or risk. Cite file:line. One paragraph.
+    allowed_tools: ["read"]
+    effort: low
+    idle_timeout: 90000
+    depends_on: [shape]
+
+  - id: improvement
+    prompt: |
+      Based on the prior weakness ($weakness.output), propose ONE
+      surgical improvement (≤6 lines of Rust). Show the patch as
+      `old_string` and `new_string` in markdown code blocks.
+    allowed_tools: []
+    effort: low
+    idle_timeout: 90000
+    depends_on: [weakness]