Shared implementation policy for model-backed session-title providers. It resolves the auxiliary route, frames exact selected human messages as JSON, applies a language-aware title instruction, enforces input and output budgets, composes timeout and caller cancellation, assembles the stream, and returns normalized text with exact source seqs and model provenance.

This package is a library, not a Cordis plugin. The provider plugins call registerSessionTitleLlmProvider() with their cadence and message selector; it validates shared config and delegates each revision to generateSessionTitleWithLlm(), so registration, route, prompt, cancellation, and validation behavior cannot drift between them.

Route and failure contract

provider and model overrides are optional but must be supplied together as non-empty strings. Without that pair, the helper uses the exact provider/model route captured from the current session's logged request/header; an explicit refresh before any route exists therefore needs overrides. Input exceeding maxInputBytes rejects instead of being truncated. Timeout, cancellation, malformed or empty output, tool calls, and non-stop finish reasons also reject; the session-title service decides whether that rejection is an automatic warning or an explicit caller failure.

Configuration

Every field is required except the paired route override; there are no library defaults.

Key	Contract
`targetWords`	Positive target word count for non-CJK titles.
`targetCjkCharacters`	Positive target character count for Chinese, Japanese, or Korean titles.
`maxInputBytes`	Positive aggregate UTF-8 byte ceiling across selected messages.
`maxOutputTokens`	Positive auxiliary generation token cap.
`timeoutMs`	Positive end-to-end deadline within the runtime timer limit.
`provider`, `model`	Optional explicit route; both or neither.

Model Experience

Auxiliary title request

What the model sees

The title model receives a fixed system instruction to return one concise unadorned title in the input language, including the configured word and CJK-character targets. Its one user message contains a JSON array of the exact selected human messages and their seqs.

Token effect

The auxiliary request consumes tokens according to selected input size and maxOutputTokens. It is separate from the main agent request and does not add title text or framing to agent history.

KV Cache effect

No main-request invalidation. Auxiliary cache reuse is provider-specific; the fixed instruction is reusable while the JSON message array changes with each revision.

Known Limitations and Deferred Work

The helper accepts text output only and rejects tool calls; structured-output adapters and provider-specific prompt variants are not exposed.
It enforces a byte ceiling for the whole selected input rather than clipping individual messages or applying a retention policy.