- Bound the shared RAG search slot to one running worker. The search that is
doing the embedding/index/GPU work now owns the admission slot until it
finishes, instead of freeing it on caller timeout while the detached worker
keeps running, which let a second search enter and stack concurrent work
behind the capacity-of-one semaphore.
- Cancel active research runs before deleting their thread, project, or all
history. Deleting cascade-drops the run row, but the worker only notices at
its next lease check, so it could keep doing model/web/RAG work for a run
that no longer exists; signalling cancel first shortens that window.
- Shield the planner prompt's conversation and question with _shield_untrusted,
matching the decision and synthesis prompts, so untrusted text cannot forge
planner delimiters.
- Do not let a research key-revocation failure replace a successful
non-streaming completion; log it like the streaming path does.
- Include created_at in the protected research-message guard so a client cannot
reorder server-managed prompt/response messages while leaving the body intact.
- Reject non-scalar ragScope values; a nested container evades the
sensitive-key scan when its inner keys are unlisted and would reach retrieval
code that expects a scalar scope id.
Adds regression tests for each.
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