refactor(google-calendar): remove redundant type aliases

The *TypeType re-exports are unnecessary since
consumers can use import type to get the type.

Co-authored-by: Ona <no-reply@ona.com>

.claude/skills/gpg-commit-signing/SKILL.md

@@ -0,0 +1,43 @@
+---
+name: gpg-commit-signing
+description: Sign git commits with GPG in non-interactive environments. Use when committing code and the `GPG_PRIVATE_KEY_PASSPHRASE` environment variable is available. Triggers on "commit", "sign commit", "GPG", "git commit -S", or any git operation requiring signed commits.
+---
+
+# GPG Commit Signing
+
+Sign commits in headless/non-interactive environments where `/dev/tty` is unavailable.
+
+## Workflow
+
+1. Check whether `GPG_PRIVATE_KEY_PASSPHRASE` is set:
+
+   ```bash
+   test -n "$GPG_PRIVATE_KEY_PASSPHRASE" && echo "available" || echo "not set"
+   ```
+
+   If not set, skip signing — commit without `-S`.
+
+2. Try a direct signed commit first — the environment may already have loopback pinentry configured:
+
+   ```bash
+   git commit -S -m "message"
+   ```
+
+   If this succeeds, no further steps are needed.
+
+3. If step 2 fails with a `/dev/tty` error, use `--pinentry-mode loopback` via a wrapper script:
+
+   ```bash
+   printf '#!/bin/sh\ngpg --batch --pinentry-mode loopback --passphrase "$GPG_PRIVATE_KEY_PASSPHRASE" "$@"\n' > /tmp/gpg-sign.sh
+   chmod +x /tmp/gpg-sign.sh
+   git -c gpg.program=/tmp/gpg-sign.sh commit -S -m "message"
+   rm /tmp/gpg-sign.sh
+   ```
+
+   This passes the passphrase directly to gpg on each signing invocation, bypassing the need for a configured gpg-agent.
+
+## Anti-patterns
+
+- Do not echo or log `GPG_PRIVATE_KEY_PASSPHRASE`.
+- Do not commit without `-S` when the passphrase is available — the project expects signed commits.
+- Do not leave wrapper scripts on disk after committing.

packages/aris-core/src/feed-engine.ts

@@ -1,6 +1,7 @@
 import type { ActionDefinition } from "./action"
 import type { Context } from "./context"
 import type { FeedItem } from "./feed"
+import type { FeedPostProcessor, ItemGroup } from "./feed-post-processor"
 import type { FeedSource } from "./feed-source"
 
 export interface SourceError {
@@ -12,6 +13,8 @@ export interface FeedResult<TItem extends FeedItem = FeedItem> {
 	context: Context
 	items: TItem[]
 	errors: SourceError[]
+	/** Item groups produced by post-processors */
+	groupedItems?: ItemGroup[]
 }
 
 export type FeedSubscriber<TItem extends FeedItem = FeedItem> = (result: FeedResult<TItem>) => void
@@ -66,6 +69,7 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 	private subscribers = new Set<FeedSubscriber<TItems>>()
 	private cleanups: Array<() => void> = []
 	private started = false
+	private postProcessors: FeedPostProcessor[] = []
 
 	private readonly cacheTtlMs: number
 	private cachedResult: FeedResult<TItems> | null = null
@@ -108,6 +112,23 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		return this
 	}
 
+	/**
+	 * Registers a post-processor. Processors run in registration order
+	 * after items are collected, on every update path.
+	 */
+	registerPostProcessor(processor: FeedPostProcessor): this {
+		this.postProcessors.push(processor)
+		return this
+	}
+
+	/**
+	 * Unregisters a post-processor by reference.
+	 */
+	unregisterPostProcessor(processor: FeedPostProcessor): this {
+		this.postProcessors = this.postProcessors.filter((p) => p !== processor)
+		return this
+	}
+
 	/**
 	 * Refreshes the feed by running all sources in dependency order.
 	 * Calls fetchContext() then fetchItems() on each source.
@@ -152,7 +173,18 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 
 		this.context = context
 
-		const result: FeedResult<TItems> = { context, items: items as TItems[], errors }
+		const {
+			items: processedItems,
+			groupedItems,
+			errors: postProcessorErrors,
+		} = await this.applyPostProcessors(items as TItems[], context, errors)
+
+		const result: FeedResult<TItems> = {
+			context,
+			items: processedItems,
+			errors: postProcessorErrors,
+			...(groupedItems.length > 0 ? { groupedItems } : {}),
+		}
 		this.updateCache(result)
 
 		return result
@@ -260,6 +292,72 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 		return actions
 	}
 
+	private async applyPostProcessors(
+		items: TItems[],
+		context: Context,
+		errors: SourceError[],
+	): Promise<{ items: TItems[]; groupedItems: ItemGroup[]; errors: SourceError[] }> {
+		let currentItems = items
+		const allGroupedItems: ItemGroup[] = []
+		const allErrors = [...errors]
+		const boostScores = new Map<string, number>()
+
+		for (const processor of this.postProcessors) {
+			const snapshot = currentItems
+			try {
+				const enhancement = await processor(currentItems, context)
+
+				if (enhancement.additionalItems?.length) {
+					// Post-processors operate on FeedItem[] without knowledge of TItems.
+					// Additional items are merged untyped — this is intentional. The
+					// processor contract is "FeedItem in, FeedItem out"; type narrowing
+					// is the caller's responsibility when consuming FeedResult.
+					currentItems = [...currentItems, ...(enhancement.additionalItems as TItems[])]
+				}
+
+				if (enhancement.suppress?.length) {
+					const suppressSet = new Set(enhancement.suppress)
+					currentItems = currentItems.filter((item) => !suppressSet.has(item.id))
+				}
+
+				if (enhancement.groupedItems?.length) {
+					allGroupedItems.push(...enhancement.groupedItems)
+				}
+
+				if (enhancement.boost) {
+					for (const [id, score] of Object.entries(enhancement.boost)) {
+						boostScores.set(id, (boostScores.get(id) ?? 0) + score)
+					}
+				}
+			} catch (err) {
+				const sourceId = processor.name || "anonymous"
+				allErrors.push({
+					sourceId,
+					error: err instanceof Error ? err : new Error(String(err)),
+				})
+				currentItems = snapshot
+			}
+		}
+
+		// Apply boost reordering: positive-boost first (desc), then zero, then negative (desc).
+		// Stable sort within each tier preserves original relative order.
+		if (boostScores.size > 0) {
+			currentItems = applyBoostOrder(currentItems, boostScores)
+		}
+
+		// Remove stale item IDs from groups and drop empty groups
+		const itemIds = new Set(currentItems.map((item) => item.id))
+		const validGroups = allGroupedItems.reduce<ItemGroup[]>((acc, group) => {
+			const ids = group.itemIds.filter((id) => itemIds.has(id))
+			if (ids.length > 0) {
+				acc.push({ ...group, itemIds: ids })
+			}
+			return acc
+		}, [])
+
+		return { items: currentItems, groupedItems: validGroups, errors: allErrors }
+	}
+
 	private ensureGraph(): SourceGraph {
 		if (!this.graph) {
 			this.graph = buildGraph(Array.from(this.sources.values()))
@@ -311,10 +409,17 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 			}
 		}
 
+		const {
+			items: processedItems,
+			groupedItems,
+			errors: postProcessorErrors,
+		} = await this.applyPostProcessors(items as TItems[], this.context, errors)
+
 		const result: FeedResult<TItems> = {
 			context: this.context,
-			items: items as TItems[],
-			errors,
+			items: processedItems,
+			errors: postProcessorErrors,
+			...(groupedItems.length > 0 ? { groupedItems } : {}),
 		}
 		this.updateCache(result)
 
@@ -395,6 +500,47 @@ export class FeedEngine<TItems extends FeedItem = FeedItem> {
 	}
 }
 
+function clamp(value: number, min: number, max: number): number {
+	return Math.min(max, Math.max(min, value))
+}
+
+function applyBoostOrder<T extends FeedItem>(items: T[], boostScores: Map<string, number>): T[] {
+	const positive: T[] = []
+	const neutral: T[] = []
+	const negative: T[] = []
+
+	for (const item of items) {
+		const raw = boostScores.get(item.id)
+		if (raw === undefined || raw === 0) {
+			neutral.push(item)
+		} else {
+			const clamped = clamp(raw, -1, 1)
+			if (clamped > 0) {
+				positive.push(item)
+			} else if (clamped < 0) {
+				negative.push(item)
+			} else {
+				neutral.push(item)
+			}
+		}
+	}
+
+	// Sort positive descending by boost, negative descending (least negative first, most negative last)
+	positive.sort((a, b) => {
+		const aScore = clamp(boostScores.get(a.id) ?? 0, -1, 1)
+		const bScore = clamp(boostScores.get(b.id) ?? 0, -1, 1)
+		return bScore - aScore
+	})
+
+	negative.sort((a, b) => {
+		const aScore = clamp(boostScores.get(a.id) ?? 0, -1, 1)
+		const bScore = clamp(boostScores.get(b.id) ?? 0, -1, 1)
+		return bScore - aScore
+	})
+
+	return [...positive, ...neutral, ...negative]
+}
+
 function buildGraph(sources: FeedSource[]): SourceGraph {
 	const byId = new Map<string, FeedSource>()
 	for (const source of sources) {

packages/aris-core/src/feed-post-processor.test.ts

@@ -0,0 +1,596 @@
+import { describe, expect, mock, test } from "bun:test"
+
+import type { ActionDefinition, FeedItem, FeedPostProcessor, FeedSource } from "./index"
+
+import { FeedEngine } from "./feed-engine"
+import { UnknownActionError } from "./index"
+
+// No-op action methods for test sources
+const noActions = {
+	async listActions(): Promise<Record<string, ActionDefinition>> {
+		return {}
+	},
+	async executeAction(actionId: string): Promise<void> {
+		throw new UnknownActionError(actionId)
+	},
+}
+
+// =============================================================================
+// FEED ITEMS
+// =============================================================================
+
+type WeatherItem = FeedItem<"weather", { temp: number }>
+type CalendarItem = FeedItem<"calendar", { title: string }>
+
+function weatherItem(id: string, temp: number): WeatherItem {
+	return { id, type: "weather", timestamp: new Date(), data: { temp } }
+}
+
+function calendarItem(id: string, title: string): CalendarItem {
+	return { id, type: "calendar", timestamp: new Date(), data: { title } }
+}
+
+// =============================================================================
+// TEST SOURCES
+// =============================================================================
+
+function createWeatherSource(items: WeatherItem[]) {
+	return {
+		id: "aris.weather",
+		...noActions,
+		async fetchContext() {
+			return null
+		},
+		async fetchItems(): Promise<WeatherItem[]> {
+			return items
+		},
+	}
+}
+
+function createCalendarSource(items: CalendarItem[]) {
+	return {
+		id: "aris.calendar",
+		...noActions,
+		async fetchContext() {
+			return null
+		},
+		async fetchItems(): Promise<CalendarItem[]> {
+			return items
+		},
+	}
+}
+
+// =============================================================================
+// REGISTRATION
+// =============================================================================
+
+describe("FeedPostProcessor", () => {
+	describe("registration", () => {
+		test("registerPostProcessor is chainable", () => {
+			const engine = new FeedEngine()
+			const processor: FeedPostProcessor = async () => ({})
+			const result = engine.registerPostProcessor(processor)
+			expect(result).toBe(engine)
+		})
+
+		test("unregisterPostProcessor is chainable", () => {
+			const engine = new FeedEngine()
+			const processor: FeedPostProcessor = async () => ({})
+			const result = engine.unregisterPostProcessor(processor)
+			expect(result).toBe(engine)
+		})
+
+		test("unregistered processor does not run", async () => {
+			const processor = mock(async () => ({}))
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(processor)
+				.unregisterPostProcessor(processor)
+
+			await engine.refresh()
+			expect(processor).not.toHaveBeenCalled()
+		})
+	})
+
+	// =============================================================================
+	// ADDITIONAL ITEMS
+	// =============================================================================
+
+	describe("additionalItems", () => {
+		test("injects additional items into the feed", async () => {
+			const extra = calendarItem("c1", "Meeting")
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => ({ additionalItems: [extra] }))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(2)
+			expect(result.items.find((i) => i.id === "c1")).toBeDefined()
+		})
+	})
+
+	// =============================================================================
+	// SUPPRESS
+	// =============================================================================
+
+	describe("suppress", () => {
+		test("removes suppressed items from the feed", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ suppress: ["w1"] }))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(1)
+			expect(result.items[0].id).toBe("w2")
+		})
+
+		test("suppressing nonexistent ID is a no-op", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => ({ suppress: ["nonexistent"] }))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(1)
+		})
+	})
+
+	// =============================================================================
+	// GROUPED ITEMS
+	// =============================================================================
+
+	describe("groupedItems", () => {
+		test("accumulates grouped items on FeedResult", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createCalendarSource([calendarItem("c1", "Meeting A"), calendarItem("c2", "Meeting B")]),
+				)
+				.registerPostProcessor(async () => ({
+					groupedItems: [{ itemIds: ["c1", "c2"], summary: "Busy afternoon" }],
+				}))
+
+			const result = await engine.refresh()
+			expect(result.groupedItems).toEqual([{ itemIds: ["c1", "c2"], summary: "Busy afternoon" }])
+		})
+
+		test("multiple processors accumulate groups", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createCalendarSource([calendarItem("c1", "Meeting A"), calendarItem("c2", "Meeting B")]),
+				)
+				.registerPostProcessor(async () => ({
+					groupedItems: [{ itemIds: ["c1"], summary: "Group A" }],
+				}))
+				.registerPostProcessor(async () => ({
+					groupedItems: [{ itemIds: ["c2"], summary: "Group B" }],
+				}))
+
+			const result = await engine.refresh()
+			expect(result.groupedItems).toEqual([
+				{ itemIds: ["c1"], summary: "Group A" },
+				{ itemIds: ["c2"], summary: "Group B" },
+			])
+		})
+
+		test("stale item IDs are removed from groups after suppression", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createCalendarSource([calendarItem("c1", "Meeting A"), calendarItem("c2", "Meeting B")]),
+				)
+				.registerPostProcessor(async () => ({
+					groupedItems: [{ itemIds: ["c1", "c2"], summary: "Afternoon" }],
+				}))
+				.registerPostProcessor(async () => ({ suppress: ["c1"] }))
+
+			const result = await engine.refresh()
+			expect(result.groupedItems).toEqual([{ itemIds: ["c2"], summary: "Afternoon" }])
+		})
+
+		test("groups with all items suppressed are dropped", async () => {
+			const engine = new FeedEngine()
+				.register(createCalendarSource([calendarItem("c1", "Meeting A")]))
+				.registerPostProcessor(async () => ({
+					groupedItems: [{ itemIds: ["c1"], summary: "Solo" }],
+				}))
+				.registerPostProcessor(async () => ({ suppress: ["c1"] }))
+
+			const result = await engine.refresh()
+			expect(result.groupedItems).toBeUndefined()
+		})
+
+		test("groupedItems is omitted when no processors produce groups", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => ({}))
+
+			const result = await engine.refresh()
+			expect(result.groupedItems).toBeUndefined()
+		})
+	})
+
+	// =============================================================================
+	// BOOST
+	// =============================================================================
+
+	describe("boost", () => {
+		test("positive boost moves item before non-boosted items", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ boost: { w2: 0.8 } }))
+
+			const result = await engine.refresh()
+			expect(result.items.map((i) => i.id)).toEqual(["w2", "w1"])
+		})
+
+		test("negative boost moves item after non-boosted items", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ boost: { w1: -0.5 } }))
+
+			const result = await engine.refresh()
+			expect(result.items.map((i) => i.id)).toEqual(["w2", "w1"])
+		})
+
+		test("multiple boosted items are sorted by boost descending", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createWeatherSource([
+						weatherItem("w1", 20),
+						weatherItem("w2", 25),
+						weatherItem("w3", 30),
+					]),
+				)
+				.registerPostProcessor(async () => ({
+					boost: { w3: 0.3, w1: 0.9 },
+				}))
+
+			const result = await engine.refresh()
+			// w1 (0.9) first, w3 (0.3) second, w2 (no boost) last
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "w3", "w2"])
+		})
+
+		test("multiple processors accumulate boost scores", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ boost: { w1: 0.3 } }))
+				.registerPostProcessor(async () => ({ boost: { w1: 0.4 } }))
+
+			const result = await engine.refresh()
+			// w1 accumulated boost = 0.7, moves before w2
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "w2"])
+		})
+
+		test("accumulated boost is clamped to [-1, 1]", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createWeatherSource([
+						weatherItem("w1", 20),
+						weatherItem("w2", 25),
+						weatherItem("w3", 30),
+					]),
+				)
+				.registerPostProcessor(async () => ({ boost: { w1: 0.8, w2: 0.9 } }))
+				.registerPostProcessor(async () => ({ boost: { w1: 0.8 } }))
+
+			const result = await engine.refresh()
+			// w1 accumulated = 1.6 clamped to 1, w2 = 0.9 — w1 still first
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "w2", "w3"])
+		})
+
+		test("out-of-range boost values are clamped", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ boost: { w1: 5.0 } }))
+
+			const result = await engine.refresh()
+			// Clamped to 1, still boosted to front
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "w2"])
+		})
+
+		test("boosting a suppressed item is a no-op", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({
+					suppress: ["w1"],
+					boost: { w1: 1.0 },
+				}))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(1)
+			expect(result.items[0].id).toBe("w2")
+		})
+
+		test("boosting a nonexistent item ID is a no-op", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => ({ boost: { nonexistent: 1.0 } }))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(1)
+			expect(result.items[0].id).toBe("w1")
+		})
+
+		test("items with equal boost retain original relative order", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createWeatherSource([
+						weatherItem("w1", 20),
+						weatherItem("w2", 25),
+						weatherItem("w3", 30),
+					]),
+				)
+				.registerPostProcessor(async () => ({
+					boost: { w1: 0.5, w3: 0.5 },
+				}))
+
+			const result = await engine.refresh()
+			// w1 and w3 have equal boost — original order preserved: w1 before w3
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "w3", "w2"])
+		})
+
+		test("negative boosts preserve relative order among demoted items", async () => {
+			const engine = new FeedEngine()
+				.register(
+					createWeatherSource([
+						weatherItem("w1", 20),
+						weatherItem("w2", 25),
+						weatherItem("w3", 30),
+					]),
+				)
+				.registerPostProcessor(async () => ({
+					boost: { w1: -0.3, w2: -0.3 },
+				}))
+
+			const result = await engine.refresh()
+			// w3 (neutral) first, then w1 and w2 (equal negative) in original order
+			expect(result.items.map((i) => i.id)).toEqual(["w3", "w1", "w2"])
+		})
+
+		test("boost works alongside additionalItems and groupedItems", async () => {
+			const extra = calendarItem("c1", "Meeting")
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({
+					additionalItems: [extra],
+					boost: { c1: 1.0 },
+					groupedItems: [{ itemIds: ["w1", "c1"], summary: "Related" }],
+				}))
+
+			const result = await engine.refresh()
+			// c1 boosted to front
+			expect(result.items[0].id).toBe("c1")
+			expect(result.items).toHaveLength(3)
+			expect(result.groupedItems).toEqual([{ itemIds: ["w1", "c1"], summary: "Related" }])
+		})
+	})
+
+	// =============================================================================
+	// PIPELINE ORDERING
+	// =============================================================================
+
+	describe("pipeline ordering", () => {
+		test("each processor sees items as modified by the previous processor", async () => {
+			const seen: string[] = []
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => ({
+					additionalItems: [calendarItem("c1", "Injected")],
+				}))
+				.registerPostProcessor(async (items) => {
+					seen.push(...items.map((i) => i.id))
+					return {}
+				})
+
+			await engine.refresh()
+			expect(seen).toEqual(["w1", "c1"])
+		})
+
+		test("suppression in first processor affects second processor", async () => {
+			const seen: string[] = []
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({ suppress: ["w1"] }))
+				.registerPostProcessor(async (items) => {
+					seen.push(...items.map((i) => i.id))
+					return {}
+				})
+
+			await engine.refresh()
+			expect(seen).toEqual(["w2"])
+		})
+	})
+
+	// =============================================================================
+	// ERROR HANDLING
+	// =============================================================================
+
+	describe("error handling", () => {
+		test("throwing processor is recorded in errors and pipeline continues", async () => {
+			const seen: string[] = []
+
+			async function failingProcessor(): Promise<never> {
+				throw new Error("processor failed")
+			}
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(failingProcessor)
+				.registerPostProcessor(async (items) => {
+					seen.push(...items.map((i) => i.id))
+					return {}
+				})
+
+			const result = await engine.refresh()
+
+			const ppError = result.errors.find((e) => e.sourceId === "failingProcessor")
+			expect(ppError).toBeDefined()
+			expect(ppError!.error.message).toBe("processor failed")
+
+			// Pipeline continued — observer still saw the original item
+			expect(seen).toEqual(["w1"])
+			expect(result.items).toHaveLength(1)
+		})
+
+		test("anonymous throwing processor uses 'anonymous' as sourceId", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(async () => {
+					throw new Error("anon failed")
+				})
+
+			const result = await engine.refresh()
+			const ppError = result.errors.find((e) => e.sourceId === "anonymous")
+			expect(ppError).toBeDefined()
+		})
+
+		test("non-Error throw is wrapped", async () => {
+			async function failingProcessor(): Promise<never> {
+				throw "string error"
+			}
+
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20)]))
+				.registerPostProcessor(failingProcessor)
+
+			const result = await engine.refresh()
+			const ppError = result.errors.find((e) => e.sourceId === "failingProcessor")
+			expect(ppError).toBeDefined()
+			expect(ppError!.error).toBeInstanceOf(Error)
+		})
+	})
+
+	// =============================================================================
+	// REACTIVE PATHS
+	// =============================================================================
+
+	describe("reactive updates", () => {
+		test("post-processors run during reactive context updates", async () => {
+			let callCount = 0
+
+			let triggerUpdate: ((update: Record<string, unknown>) => void) | null = null
+
+			const source: FeedSource = {
+				id: "aris.reactive",
+				...noActions,
+				async fetchContext() {
+					return null
+				},
+				async fetchItems() {
+					return [weatherItem("w1", 20)]
+				},
+				onContextUpdate(callback, _getContext) {
+					triggerUpdate = callback
+					return () => {
+						triggerUpdate = null
+					}
+				},
+			}
+
+			const engine = new FeedEngine().register(source).registerPostProcessor(async () => {
+				callCount++
+				return {}
+			})
+
+			engine.start()
+
+			// Wait for initial periodic refresh
+			await new Promise((resolve) => setTimeout(resolve, 50))
+			const countAfterStart = callCount
+
+			// Trigger a reactive context update
+			triggerUpdate!({ foo: "bar" })
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			expect(callCount).toBeGreaterThan(countAfterStart)
+
+			engine.stop()
+		})
+
+		test("post-processors run during reactive item updates", async () => {
+			let callCount = 0
+
+			let triggerItemsUpdate: (() => void) | null = null
+
+			const source: FeedSource = {
+				id: "aris.reactive",
+				...noActions,
+				async fetchContext() {
+					return null
+				},
+				async fetchItems() {
+					return [weatherItem("w1", 20)]
+				},
+				onItemsUpdate(callback, _getContext) {
+					triggerItemsUpdate = callback
+					return () => {
+						triggerItemsUpdate = null
+					}
+				},
+			}
+
+			const engine = new FeedEngine().register(source).registerPostProcessor(async () => {
+				callCount++
+				return {}
+			})
+
+			engine.start()
+
+			await new Promise((resolve) => setTimeout(resolve, 50))
+			const countAfterStart = callCount
+
+			// Trigger a reactive items update
+			triggerItemsUpdate!()
+			await new Promise((resolve) => setTimeout(resolve, 50))
+
+			expect(callCount).toBeGreaterThan(countAfterStart)
+
+			engine.stop()
+		})
+	})
+
+	// =============================================================================
+	// NO PROCESSORS = NO CHANGE
+	// =============================================================================
+
+	describe("no processors", () => {
+		test("engine without post-processors returns raw items unchanged", async () => {
+			const items = [weatherItem("w1", 20), weatherItem("w2", 25)]
+			const engine = new FeedEngine().register(createWeatherSource(items))
+
+			const result = await engine.refresh()
+			expect(result.items).toHaveLength(2)
+			expect(result.items[0].id).toBe("w1")
+			expect(result.items[1].id).toBe("w2")
+			expect(result.groupedItems).toBeUndefined()
+		})
+	})
+
+	// =============================================================================
+	// COMBINED ENHANCEMENT
+	// =============================================================================
+
+	describe("combined enhancement", () => {
+		test("single processor can use all enhancement fields at once", async () => {
+			const engine = new FeedEngine()
+				.register(createWeatherSource([weatherItem("w1", 20), weatherItem("w2", 25)]))
+				.registerPostProcessor(async () => ({
+					additionalItems: [calendarItem("c1", "Injected")],
+					suppress: ["w2"],
+					groupedItems: [{ itemIds: ["w1", "c1"], summary: "Related" }],
+				}))
+
+			const result = await engine.refresh()
+
+			// w2 suppressed, c1 injected → w1 + c1
+			expect(result.items).toHaveLength(2)
+			expect(result.items.map((i) => i.id)).toEqual(["w1", "c1"])
+
+			// Groups on result
+			expect(result.groupedItems).toEqual([{ itemIds: ["w1", "c1"], summary: "Related" }])
+		})
+	})
+})

packages/aris-core/src/feed-post-processor.ts

@@ -0,0 +1,26 @@
+import type { Context } from "./context"
+import type { FeedItem } from "./feed"
+
+export interface ItemGroup {
+	/** IDs of items to present together */
+	itemIds: string[]
+	/** Summary text for the group */
+	summary: string
+}
+
+export interface FeedEnhancement {
+	/** New items to inject into the feed */
+	additionalItems?: FeedItem[]
+	/** Groups of items to present together with a summary */
+	groupedItems?: ItemGroup[]
+	/** Item IDs to remove from the feed */
+	suppress?: string[]
+	/** Map of item ID to boost score (-1 to 1). Positive promotes, negative demotes. */
+	boost?: Record<string, number>
+}
+
+/**
+ * A function that transforms feed items and produces enhancement directives.
+ * Use named functions for meaningful error attribution.
+ */
+export type FeedPostProcessor = (items: FeedItem[], context: Context) => Promise<FeedEnhancement>

packages/aris-core/src/index.ts

@@ -13,6 +13,9 @@ export { TimeRelevance } from "./feed"
 // Feed Source
 export type { FeedSource } from "./feed-source"
 
+// Feed Post-Processor
+export type { FeedEnhancement, FeedPostProcessor, ItemGroup } from "./feed-post-processor"
+
 // Feed Engine
 export type { FeedEngineConfig, FeedResult, FeedSubscriber, SourceError } from "./feed-engine"
 export { FeedEngine } from "./feed-engine"

packages/aris-source-google-calendar/src/index.ts

@@ -1,7 +1,6 @@
 export { NextEventKey, type NextEvent } from "./calendar-context"
 export {
 	CalendarFeedItemType,
-	type CalendarFeedItemType as CalendarFeedItemTypeType,
 	type CalendarAllDayFeedItem,
 	type CalendarEventFeedItem,
 	type CalendarFeedItem,
@@ -10,7 +9,6 @@ export { DefaultGoogleCalendarClient } from "./google-calendar-api"
 export { GoogleCalendarSource, type GoogleCalendarSourceOptions } from "./google-calendar-source"
 export {
 	EventStatus,
-	type EventStatus as EventStatusType,
 	type ApiCalendarEvent,
 	type ApiEventDateTime,
 	type CalendarEventData,