[DOC] ADR-0008: add formal routing contract (RC-01 to RC-06)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/ADR/ADR-0008-adaptive-query-routing-intent-history.md

@@ -77,6 +77,81 @@ Queries containing `"you are a direct and concise assistant"` (a system-injected
 
 ---
 
+## Routing Contract
+
+This section is normative. Any reimplementation of the classifier or the graph must satisfy all rules below. Rules are ordered by priority — a higher-priority rule always wins.
+
+### RC-01 — Fast-path override (priority: highest)
+
+If the query contains a known platform-injected prefix, the system **MUST** classify it as `PLATFORM` without invoking any LLM.
+
+```
+∀ q : query
+  contains(q, known_platform_prefix) → route(q) = PLATFORM
+```
+
+Current registered prefixes (see `_PLATFORM_PATTERNS` in `graph.py`):
+- `"you are a direct and concise assistant"`
+
+Adding a new prefix requires a code change to `_PLATFORM_PATTERNS` and a corresponding update to this list.
+
+### RC-02 — Platform data signal (priority: high)
+
+If the query contains any of the following signals, the classifier **MUST** output `PLATFORM` regardless of conversation history:
+
+- Usage percentages (e.g. `"20%"` in the context of project/account usage)
+- Account metrics or consumption figures
+- Quota, limit, or billing data
+
+This rule is enforced via `<platform_priority_rule>` in the classifier prompt. It cannot be overridden by history.
+
+### RC-03 — Intent history scoping (priority: medium)
+
+The classifier **MUST** use `classify_history` only to resolve ambiguous pronoun or deictic references (`"this"`, `"esto"`, `"lo anterior"`, `"that function"`). It **MUST NOT** use history to predict or bias the type of the current message.
+
+```
+classify(q, history) ≠ f(dominant_type(history))
+classify(q, history) = f(intent(q), resolve_references(q, history))
+```
+
+### RC-04 — RAG bypass (priority: medium)
+
+Query types that bypass Elasticsearch retrieval:
+
+| Type | RAG | Justification |
+|---|---|---|
+| `RETRIEVAL` | Yes | Requires documentation context |
+| `CODE_GENERATION` | Yes | Requires syntax examples |
+| `CONVERSATIONAL` | No | Reformulates prior answer already in context |
+| `PLATFORM` | No | Data is injected via `extra_context`, not retrieved |
+
+A `PLATFORM` or `CONVERSATIONAL` query that triggers a retrieval step is a contract violation.
+
+### RC-05 — Model assignment (priority: medium)
+
+```
+route(q) ∈ {RETRIEVAL, CODE_GENERATION} → model = OLLAMA_MODEL_NAME
+route(q) ∈ {CONVERSATIONAL, PLATFORM}   → model = OLLAMA_MODEL_NAME_CONVERSATIONAL
+                                                    ?? OLLAMA_MODEL_NAME  # fallback if unset
+```
+
+Changing which types map to which model slot requires updating this contract.
+
+### RC-06 — History growth bound (priority: low)
+
+`classify_history` per session **MUST** be bounded. The classifier reads at most the last 6 entries. The store may grow unbounded in memory but the classifier input is always capped.
+
+### Contract violations to monitor
+
+| Symptom | Violated rule |
+|---|---|
+| Platform query hits Elasticsearch | RC-04 |
+| `qwen3:1.7b` used for a `PLATFORM` response | RC-05 |
+| Platform prefix query triggers LLM classifier | RC-01 |
+| Classifier output mirrors dominant history type | RC-03 |
+
+---
+
 ## Consequences
 
 ### Positive