fix(server,acp): diff cache eviction, ACP elicitation, permission approvals, and preview recovery (#685)

[rynfar]

Upstream integration cycle (Group B):
Part of #685

This PR ports and hardens Group B items from upstream:

• #12523: Release oversized pull request diff cache entries, with uninterruptible eviction hardening.
• #11294: Accept ACP SDK elicitation requests (session/elicitation and elicitation/create).
• #7861: Surface Codex app permission requests as approvable, hardened against acceptAlways permission erasure and retirement/recovery boundaries.
• #12535: Recover preview host registration after request timeouts via connection queue eviction.
• Clean up mobile AppSymbol icon mapping.
• Rebrand pre-existing T3 Code references in PR tool description to Pylon.

Monorepo typechecks and all unit tests pass.

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Project	Deployment	Actions	Updated
pylon-marketing	Building	Preview	Sep 20, 2026 7:56pm UTC