* refactor(model-routing): centralize explicit foreground fallback policy
Make foreground fallback an explicit per-user, availability-only policy shared by streaming Chat, non-stream Chat, and Agent runs.
Preserve strict defaults, owner/model and credential boundaries, pinned Agent routes, and truthful per-round provenance/accounting. Carry provider-reported model identifiers through native streaming adapters, non-stream responses, and caches, and keep legacy default_model_fallbacks as tombstoned raw storage that generic settings APIs and agent tools cannot expose or mutate.
* fix(agent-loop): restore rebase-dropped qwen routing, workspace prompt, and temperature clamp
* fix(model-routing): thread selected endpoint identity, fix cost classification and fallback eligibility
* fix(chat): restore stream helpers and harden run stop lifecycle
* fix(model-routing): let numeric provider codes win over symbolic rate-limit statuses
* fix(agent-loop): apply qwen temperature and notes-tool clamps per fallback candidate
* fix(chat): honor queued stop across resend and reload canonical terminal on EOF
* fix(chat): track stop queue and cleanup ownership by per-send generation
* fix(agent-loop): preserve requested temperature for non-qwen fallback candidates
* fix(chat): reserve send ownership before any await and scope stop to the current send
* fix(chat): clear the previous run identity at send reservation
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Co-authored-by: RaresKeY <158580472+RaresKeY@users.noreply.github.com>
Co-authored-by: StressTestor <212606152+StressTestor@users.noreply.github.com>
