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fix(core): share child prompt cache affinity #50495

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Merged
rekram1-node merged 1 commit into from
Sep 22, 2026
Merged

fix(core): share child prompt cache affinity #50495

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4 changes: 2 additions & 2 deletions packages/core/src/session/model-request.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -229,7 +229,7 @@ export const layer = Layer.effect(
const entries = Object.entries(shaped.options)
const generation = Object.fromEntries(entries.filter(([k]) => GENERATION_KEYS.has(k))) as GenerationOptionsFields
const providerOptions = Object.fromEntries(entries.filter(([k]) => !GENERATION_KEYS.has(k)))
const root = session.fork?.sessionID ?? session.id
const affinity = session.parentID ?? session.fork?.sessionID ?? session.id
const base = LLM.request({
model: model.model,
http: {
Expand All @@ -244,7 +244,7 @@ export const layer = Layer.effect(
},
},
// TODO: Persist cache lineage so nested forks reuse the root session's cache key.
promptCacheKey: /^ses_[0-9a-f]{64}$/.test(root) ? root.slice(4) : root,
promptCacheKey: /^ses_[0-9a-f]{64}$/.test(affinity) ? affinity.slice(4) : affinity,
system: shaped.system,
messages: boundImages(unsupportedParts(shaped.messages, model.capabilities)),
tools: Array.from(hooked, ([name, t]) => ({ ...t, name })),
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2 changes: 1 addition & 1 deletion packages/core/test/session-compaction.test.ts
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Expand Up @@ -397,7 +397,7 @@ it.effect("manual compaction summarizes short context instead of no-op", () =>
])

expect(requests).toHaveLength(1)
expect(requests[0]?.promptCacheKey).toBe(sessionID)
expect(requests[0]?.promptCacheKey).toBe(parentID)
expect(requests[0]?.http?.headers).toEqual({
"x-session-affinity": sessionID,
"X-Session-Id": sessionID,
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3 changes: 2 additions & 1 deletion packages/core/test/session-runner.test.ts
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Expand Up @@ -4411,7 +4411,7 @@ describe("SessionRunnerLLM", () => {
})
})

scenario("adds the parent session header to child model requests", function* (s) {
scenario("uses parent cache affinity for child model requests", function* (s) {
const parentID = Session.ID.make("ses_runner_parent")

yield* s.db
Expand All @@ -4423,6 +4423,7 @@ describe("SessionRunnerLLM", () => {
yield* s.runPrompt("Run child request")

expect(s.requests[0]?.http?.headers?.["x-parent-session-id"]).toBe(parentID)
expect(s.requests[0]?.promptCacheKey).toBe(parentID)
})

scenario("runs different sessions concurrently", function* (s) {
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