[Feature]: thread locking

[Nintorac]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/server

Problem or use case

I find myself dumping dollars on a request when i come back after too long and the tokens have dropped out of cache

Proposed solution

I want a lock feature on threads that make it read only. And a stretch goal I want threads to autolock after cache is dead. There should be a manual workaround for resuming a locked thread. The UI could also provide an indicator of the cost to resume the conversation

Why this matters

This can save accidental large conversations from being fully reprocessed, reducing costs and increasing efficiency.

Aside, it also provides a convenient "end of session" boundary that doesn't really exist in t3code and is something some automation I have built around codex/cc rely on.

Smallest useful scope

• A lock feature in the UI
• Option to autolock threads after a period of time

Alternatives considered

I currently work around this by manually avoiding large old conversations

Risks or tradeoffs

Difficult to track cache liveness and resume costs across providers.

Examples or references

No response

Contribution

• I would be open to helping implement this.