Summary

After the session key fix, fallback removal, and cost removal, resolveDefaultModel() and the provider/model variables in get-reply.ts and get-reply-run.ts serve no purpose. The only meaningful identifier is the runtime name from resolveAgentRuntimeOrThrow().

What to Remove/Simplify

• Delete resolveDefaultModel() from directive-handling.persist.ts
• Remove defaultProvider, defaultModel, aliasIndex from get-reply.ts
• Remove provider, model params from RunPreparedReplyParams in get-reply-run.ts
• Replace all downstream uses with runtimeId sourced from resolveAgentRuntimeOrThrow()
• Remove parseModelRef() calls (no model references to parse)
• Remove channel model override logic (resolveChannelModelOverride)

Acceptance Criteria

• Given the codebase
  When searching for resolveDefaultModel
  Then no results found

• Given get-reply.ts
  When inspecting the provider/model flow
  Then a single runtimeId flows from config to session usage

• pnpm check passes

• Existing tests pass (or updated)

Depends On

• Cost calculation removal (gut(session): remove vestigial model cost calculation #2107)