@spec extract_from_prompt(String.t() | nil) :: {:ok, String.t()} | :none

Attempt to extract an engine preference from the beginning of a prompt.

Returns {:ok, engine_id} if a known engine switch pattern is found, or :none if no engine preference is detected.

Patterns matched

• "use <engine>"
• "switch to <engine>"
• "with <engine>"

These are matched case-insensitively and only at the start of the prompt (with optional leading whitespace).

@spec resolve(map()) :: {String.t() | nil, map()}

Apply sticky engine logic for a run.

Given the current session config, the run's explicit engine_id, and the prompt, determines the effective engine_id and any updates to the session policy.

Returns {effective_engine_id, session_updates} where:

• effective_engine_id is the engine to use for this run (or nil for default)
• session_updates is a map to merge into session policy (may contain :preferred_engine)