Gateway Routing Engine

v4.2 Sprint C adds a pure deterministic route planning engine on top of the runtime registry snapshot.

This is dry-run planning only:

• no provider is contacted
• no model request is executed
• no fallback attempt is executed
• no provider credentials are read
• no HTTP server is started
• no tokenization or live pricing lookup is performed

Inputs

The router consumes:

• a Sprint B gateway registry snapshot
• a routing request
• an optional routing preset ID
• an optional caller policy
• caller-supplied request ID and decision timestamp

The resolver does not implicitly load registries. Callers provide the snapshot explicitly.

Output

resolveGatewayRoute() returns a Sprint A route decision shape:

selected_provider
selected_model
strategy
score
reasons
rejected_candidates
fallback_chain
warnings
request_id
decision_timestamp
explanation

dryRunGatewayRoute() wraps the decision:

mode: dry-run
executed: false

executed is always false in Sprint C.

Safety

Explanations are planning records. They do not include prompt bodies, credential values, authorization headers, or absolute local paths.

The router uses only static metadata and caller-supplied estimates.

Current Scope

Sprint C supports:

• explicit provider/model selection
• alias resolution
• capability filtering
• context-window filtering
• provider/model exclusions
• local-only and local-preferred planning
• cost-first planning from static cost metadata
• latency-first planning from static latency hints
• context-aware planning
• balanced deterministic scoring
• user-policy weights
• fallback-chain planning without execution

Sprint D adds simulation contracts for retry, timeout, fallback transition, rate-limit, quota, and circuit-breaker planning. Provider invocation remains reserved for later gateway runtime work.

Sprint E uses only mock-provider execution. It does not execute Sprint C fallback chains or route to external registry providers.