llm: LlmCallConfig + callConfigEquals + deepFreeze — the stateless request vocabulary

The call configuration (model + sampling scalars) becomes named
vocabulary: per-conversation state that the session log records as part
of the request header (the reconstructability RFC on this branch), with
callConfigEquals as the real-change detector behind logged header deltas
and deepFreeze as the ownership helper the loop applies to every built
request. dsh-llm stays stateless — request in, chunks out; no
conversation object lives here.

packages/llm/llm/README.md

@@ -29,6 +29,10 @@ Messages are arrays of typed content blocks: `text`, `reasoning`, `tool-call`, `
 
 Streaming is a raw chunk protocol (`block-start`, `text-delta`, `reasoning-delta`, `tool-call-delta`, `block-end`, `usage`, `finish`). `BlockAssembler` is the single shared implementation that assembles chunks into blocks/messages.
 
+### Call configuration (`call-config.ts`)
+
+`LlmCallConfig` is the model + sampling scalars of one conversation's requests (`model`, `temperature`, `maxTokens`, `stop` — each mapping 1:1 onto the same-named `GenerateOptions` field). It is per-conversation state recorded in the session log as part of the request header (see the dsh-session `request/header` events), never a silently-adjustable per-call knob: the `agent/request` waterfall proposes a replacement and the loop logs a real change. `callConfigEquals(a, b)` is the field-wise real-change detector; `deepFreeze(value)` is the ownership helper the loop applies to every built request before dispatch (`llm/stream` listeners and adapters read, never rewrite).
+
 ### App attribution (`attribution.ts`)
 
 Every product adapter must identify the application on every provider HTTP request - attribution is part of the adapter contract, not an adapter-local nicety. `attributionHeaders(identity?)` builds the standard `User-Agent` header (`product/version (+url)`, from `userAgent()`) for every request. The default `APP_IDENTITY` carries only static public product facts (its version is read from this package's manifest); a white-label deployment passes its own `AppIdentity`, and omission falls back to the default - nothing can suppress attribution. OpenRouter-specific app attribution headers are intentionally not supported by this contract. An adapter proves compliance with a wire-level test: a mock server asserting the received header (or, for a library-backed adapter, that the library's header hook delivers the same value). Policy and rationale: [Mandatory `User-Agent` attribution](../../../docs/rfc/implemented/architecture/2026-06-21-mandatory-app-attribution-headers.md).

packages/llm/llm/src/call-config.ts

@@ -0,0 +1,65 @@
+/**
+ * The call configuration of a conversation and its comparison/freeze
+ * utilities. `LlmCallConfig` is the non-content third of the request header
+ * (see `EpochHeader` in dsh-session): everything about a request besides its
+ * message content that can undermine provider KV-cache reuse — `model`
+ * selects the cache namespace outright, and the sampling scalars are treated
+ * the same way out of caution. It is per-conversation state recorded in the
+ * session log (the reconstructability RFC), never a silently-drifting
+ * per-call knob: the `agent/request` waterfall proposes a replacement, and
+ * the loop logs a real change as a `request/header-delta` event.
+ *
+ * @module dsh-llm/call-config
+ */
+
+/**
+ * Model + sampling scalars of one conversation's requests. Every field maps
+ * 1:1 onto the same-named `GenerateOptions` field; the loop builds requests
+ * from the logged header rather than accepting these per call.
+ */
+export interface LlmCallConfig {
+  model: string
+  temperature?: number
+  maxTokens?: number
+  stop?: string[]
+}
+
+/**
+ * Field-wise equality over {@link LlmCallConfig} — the comparison a caller
+ * runs to decide whether a proposed configuration is a real change (worth a
+ * logged header delta) or the held one restated.
+ * @param a - one configuration.
+ * @param b - the other.
+ * @returns whether every field (including the `stop` list, element-wise) matches.
+ */
+export function callConfigEquals(a: LlmCallConfig, b: LlmCallConfig): boolean {
+  if (a.model !== b.model || a.temperature !== b.temperature || a.maxTokens !== b.maxTokens) return false
+  if (a.stop === undefined || b.stop === undefined) return a.stop === b.stop
+  return a.stop.length === b.stop.length && a.stop.every((s, i) => s === b.stop?.[i])
+}
+
+/**
+ * Deep-freeze a value in place so any later mutation throws (ESM code runs in
+ * strict mode), and return it. The loop freezes every request it builds
+ * before dispatch — `llm/stream` listeners and adapters read the request,
+ * never rewrite it, so the wire bytes cannot silently desync from what the
+ * session log reconstructs. Guards against cycles with a WeakSet: loop-built
+ * requests hold `structuredClone`d JSON-validated session data, but the
+ * helper accepts arbitrarily constructed values.
+ * @param value - the value to freeze in place.
+ * @returns the same value, frozen.
+ */
+export function deepFreeze<T>(value: T): T {
+  const seen = new WeakSet<object>()
+  const walk = (node: unknown): void => {
+    if (node === null || typeof node !== 'object') return
+    if (seen.has(node)) return
+    seen.add(node)
+    Object.freeze(node)
+    for (const key of Object.keys(node)) {
+      walk((node as Record<string, unknown>)[key])
+    }
+  }
+  walk(value)
+  return value
+}

packages/llm/llm/src/index.ts

@@ -16,6 +16,8 @@ export * from './never.ts'
 export * from './error.ts'
 export * from './types.ts'
 export { BlockAssembler } from './assembler.ts'
+export { callConfigEquals, deepFreeze } from './call-config.ts'
+export type { LlmCallConfig } from './call-config.ts'
 
 declare module 'cordis' {
   interface Context {

packages/llm/llm/tests/call-config.spec.ts

@@ -0,0 +1,44 @@
+/**
+ * call-config unit tests: field-wise LlmCallConfig equality (the real-change
+ * detector behind logged header deltas) and the deepFreeze ownership helper
+ * the loop applies to every built request.
+ */
+
+import { describe, expect, it } from 'vitest'
+import { callConfigEquals, deepFreeze } from '../src/call-config.ts'
+
+describe('callConfigEquals', () => {
+  it('compares every field, including the stop list element-wise', () => {
+    expect(callConfigEquals({ model: 'm' }, { model: 'm' })).toBe(true)
+    expect(callConfigEquals({ model: 'm' }, { model: 'x' })).toBe(false)
+    expect(callConfigEquals({ model: 'm', temperature: 0.5 }, { model: 'm' })).toBe(false)
+    expect(callConfigEquals({ model: 'm', maxTokens: 1 }, { model: 'm', maxTokens: 2 })).toBe(false)
+    expect(callConfigEquals({ model: 'm', stop: ['a'] }, { model: 'm' })).toBe(false)
+    expect(callConfigEquals({ model: 'm', stop: ['a'] }, { model: 'm', stop: ['a', 'b'] })).toBe(false)
+    expect(callConfigEquals({ model: 'm', stop: ['a'] }, { model: 'm', stop: ['b'] })).toBe(false)
+    expect(callConfigEquals({ model: 'm', stop: ['a', 'b'] }, { model: 'm', stop: ['a', 'b'] })).toBe(true)
+  })
+})
+
+describe('deepFreeze', () => {
+  it('freezes nested structure in place and returns the same reference', () => {
+    const value = { a: { b: [1, { c: 'x' }] } }
+    const frozen = deepFreeze(value)
+    expect(frozen).toBe(value)
+    expect(Object.isFrozen(value)).toBe(true)
+    expect(Object.isFrozen(value.a)).toBe(true)
+    expect(Object.isFrozen(value.a.b)).toBe(true)
+    expect(Object.isFrozen(value.a.b[1])).toBe(true)
+    // ESM runs in strict mode: mutation throws rather than silently failing.
+    expect(() => { (value.a.b[1] as { c: string }).c = 'y' }).toThrow(TypeError)
+  })
+
+  it('passes primitives through and terminates on cycles', () => {
+    expect(deepFreeze(42)).toBe(42)
+    expect(deepFreeze(null)).toBeNull()
+    const cyclic = { self: undefined as unknown }
+    cyclic.self = cyclic
+    deepFreeze(cyclic)
+    expect(Object.isFrozen(cyclic)).toBe(true)
+  })
+})