Enforce tagged constructors and Effect tag APIs

.oxlintrc.jsonc

@@ -14,7 +14,10 @@
 		"automation/no-shadowed-standard-array-static": "error",
 		"automation/no-disable-validation": "error",
 		"automation/no-silent-error-swallow": "error",
+		"automation/no-manual-tag-comparison": "error",
+		"automation/no-manual-tagged-construction": "error",
 		"automation/prefer-effect-match": "error",
+		"automation/prefer-tagged-error-handling": "error",
 		"automation/no-ambient-nondeterminism": "error",
 		"anti-slop/no-reflect-apply": "error",
 		"typescript/consistent-type-imports": ["error", { "fixStyle": "inline-type-imports" }],
@@ -73,10 +76,29 @@
 				"automation/no-disable-validation": "off",
 				"automation/no-shadowed-standard-array-static": "off",
 				"automation/no-silent-error-swallow": "off",
+				"automation/no-manual-tag-comparison": "off",
+				"automation/no-manual-tagged-construction": "off",
 				"automation/prefer-effect-match": "off",
+				"automation/prefer-tagged-error-handling": "off",
 				"automation/no-ambient-nondeterminism": "off",
 			},
 		},
+		{
+			// Runtime tagged values in tests, fixtures, and examples are often deliberate raw inputs.
+			"files": [
+				"**/test/**",
+				"**/tests/**",
+				"**/*.test.ts",
+				"**/*.test.tsx",
+				"**/*.vi.test.ts",
+				"**/*.vi.test.tsx",
+				"**/fixtures/**",
+				"**/examples/**",
+			],
+			"rules": {
+				"automation/no-manual-tagged-construction": "off",
+			},
+		},
 		{
 			// no-ambient-nondeterminism targets production seams. Tests deliberately use fixed or real
 			// time and node crypto, driven through explicit layers, so the rule is off for test files.

packages/fold-agent/examples/ApplyPatchAgent.ts

@@ -11,7 +11,7 @@ import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 
 import { defineAgent, openaiModel, startSession } from '@humanlayer/fold-core'
-import { Console, Effect } from 'effect'
+import { Predicate, Console, Effect } from 'effect'
 
 import { codingTools } from '../src/index'
 
@@ -41,7 +41,7 @@ const makeProgram = (apiKey: string) =>
 		)
 		const entries = yield* session.entries
 		const toolNames = entries.flatMap((entry) =>
-			entry._tag === 'tool-result'
+			Predicate.isTagged(entry, 'tool-result')
 				? [entry.message.content[0]?.type === 'tool-result' ? entry.message.content[0].name : '']
 				: [],
 		)

packages/fold-agent/examples/CodingAgent.ts

@@ -11,7 +11,7 @@ import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 
 import { anthropicModel, defineAgent, startSession } from '@humanlayer/fold-core'
-import { Console, Effect } from 'effect'
+import { Predicate, Console, Effect } from 'effect'
 
 import { codingTools, jsonlEventLog } from '../src/index'
 
@@ -46,7 +46,9 @@ const makeProgram = (apiKey: string) =>
 		yield* Console.log(`finished: ${finished.outcome}`)
 		yield* Console.log(`result: ${finished.resultText ?? '(no text)'}`)
 		yield* Console.log(`log rows: ${entries.length} (persisted to ${logPath})`)
-		yield* Console.log(`tools used: ${entries.filter((entry) => entry._tag === 'tool-result').length} tool results`)
+		yield* Console.log(
+			`tools used: ${entries.filter((entry) => Predicate.isTagged(entry, 'tool-result')).length} tool results`,
+		)
 	}).pipe(Effect.scoped)
 
 if (apiKey === undefined || apiKey === '') {

packages/fold-agent/examples/SubagentsAgent.ts

@@ -12,7 +12,7 @@ import { tmpdir } from 'node:os'
 import { join } from 'node:path'
 
 import { anthropicModel, defineAgent, defineSubagent, startSession, subagentTool } from '@humanlayer/fold-core'
-import { Console, Effect } from 'effect'
+import { Predicate, Console, Effect } from 'effect'
 
 import { bashTool, jsonlEventLog, readTool } from '../src/index'
 
@@ -75,14 +75,16 @@ const makeProgram = (apiKey: string) =>
 
 		// Read the story back off the durable log: one subagent, resumed under a second tool call.
 		const entries = yield* session.entries
-		const subagentStarts = entries.filter((entry) => entry._tag === 'agent_started' && entry.parentAgentId !== null)
-		const researcherId = subagentStarts[0]?._tag === 'agent_started' ? subagentStarts[0].agentId : null
+		const subagentStarts = entries.filter(
+			(entry) => Predicate.isTagged(entry, 'agent_started') && entry.parentAgentId !== null,
+		)
+		const researcherId = Predicate.isTagged(subagentStarts[0], 'agent_started') ? subagentStarts[0].agentId : null
 		const researcherTurns = entries.filter(
-			(entry) => entry._tag === 'assistant-message' && entry.agentId === researcherId,
+			(entry) => Predicate.isTagged(entry, 'assistant-message') && entry.agentId === researcherId,
 		).length
 		const researcherCalls = new Set(
 			entries
-				.filter((entry) => entry._tag === 'user-message' && entry.agentId === researcherId)
+				.filter((entry) => Predicate.isTagged(entry, 'user-message') && entry.agentId === researcherId)
 				.map((entry) => entry.toolCallId),
 		).size
 

packages/fold-agent/src/Config/ModelSelections.ts

@@ -2,7 +2,7 @@ import { DEFAULT_CODEX_MODEL_ID } from '@humanlayer/fold-codex'
 import { DEFAULT_ANTHROPIC_MODEL_ID, type ModelCatalogEntry, type FoldModel } from '@humanlayer/fold-core'
 import { DEFAULT_OPENCODE_MODEL_ID, GROK_BUILD_MODEL_ID } from '@humanlayer/fold-opencode'
 import { DEFAULT_XAI_MODEL_ID } from '@humanlayer/fold-xai'
-import { Effect, Match } from 'effect'
+import { Predicate, Effect, Match } from 'effect'
 
 import { agentModelsFromConfig, type AgentModelsOptions, RoleResolutionError } from './AgentModels'
 import type { ConfigRole, ProfileConfig, ProfileModeName, RoleBinding, FoldConfig } from './ConfigSchema'
@@ -169,7 +169,7 @@ export const resolveConfiguredModelSelection = (
 	const rootRole = roleForMode(mode)
 	return Effect.gen(function* () {
 		let roles = config.roles
-		if (selection._tag === 'profile') {
+		if (Predicate.isTagged(selection, 'profile')) {
 			const profileRoles = rolesForProfile(config, selection.profile)
 			if (profileRoles === null) {
 				return yield* new RoleResolutionError({

packages/fold-agent/src/Fs/MutationQueue.ts

@@ -26,10 +26,10 @@ const queueKey = (fs: FileSystem.FileSystem, path: string): Effect.Effect<string
 	const resolved = resolve(path)
 
 	return fs.realPath(resolved).pipe(
-		Effect.catchIf(
-			(error) => error.reason._tag === 'NotFound' || error.reason._tag === 'BadResource',
-			() => Effect.succeed(resolved),
-		),
+		Effect.catchReasons('PlatformError', {
+			NotFound: () => Effect.succeed(resolved),
+			BadResource: () => Effect.succeed(resolved),
+		}),
 	)
 }
 

packages/fold-agent/src/Mode/Launch.ts

@@ -35,7 +35,7 @@ import {
 	type FoldTool,
 	type Ids,
 } from '@humanlayer/fold-core'
-import { Effect, Match, Schema, Semaphore, type Scope } from 'effect'
+import { Predicate, Effect, Match, Schema, Semaphore, type Scope } from 'effect'
 
 import { loadModelCatalog } from '../Catalog/LoadCatalog'
 import { agentModelsFromConfig, type EnvLookup, type RoleResolutionError } from '../Config/AgentModels'
@@ -428,9 +428,12 @@ const withGeneratedTitles = (
 									Effect.flatMap((entries) => {
 										const rootUsers = entries.filter(
 											(entry) =>
-												entry._tag === 'user-message' && entry.agentId === session.rootAgentId,
+												Predicate.isTagged(entry, 'user-message') &&
+												entry.agentId === session.rootAgentId,
+										)
+										const lastTitle = entries.findLast((entry) =>
+											Predicate.isTagged(entry, 'session_title'),
 										)
-										const lastTitle = entries.findLast((entry) => entry._tag === 'session_title')
 										const generatedTurns = lastTitle?.rootUserTurns ?? 0
 										if (rootUsers.length <= generatedTurns) return Effect.void
 										return generateSessionTitle(entries, session.rootAgentId, model).pipe(

packages/fold-agent/src/Session/SessionLayout.ts

@@ -12,7 +12,7 @@ import { join } from 'node:path'
 
 import { SessionId, makeSessionId, usageInputTotal } from '@humanlayer/fold-core'
 import type { ActiveModel, LogEntry, FoldEventLog, Ids } from '@humanlayer/fold-core'
-import { Clock, Effect, Exit, Match, Option, Schema, Stream } from 'effect'
+import { Predicate, Clock, Effect, Exit, Match, Option, Schema, Stream } from 'effect'
 
 import { jsonlEventLog } from '../EventLog/JsonlDescriptor'
 import { fileSystemFor, type FsToolOptions } from '../Fs/DefaultFileSystem'
@@ -199,26 +199,26 @@ export const listSessionLogs = (options?: SessionLayoutOptions): Effect.Effect<R
 
 // Type-safe entry predicates that narrow the LogEntry union.
 const isSessionStarted = (entry: LogEntry): entry is Extract<LogEntry, { readonly _tag: 'session_started' }> =>
-	entry._tag === 'session_started'
+	Predicate.isTagged(entry, 'session_started')
 
 const isSessionTitle = (entry: LogEntry): entry is Extract<LogEntry, { readonly _tag: 'session_title' }> =>
-	entry._tag === 'session_title'
+	Predicate.isTagged(entry, 'session_title')
 
 const isUserMessage = (entry: LogEntry): entry is Extract<LogEntry, { readonly _tag: 'user-message' }> =>
-	entry._tag === 'user-message'
+	Predicate.isTagged(entry, 'user-message')
 
 const isAgentFinished = (entry: LogEntry): entry is Extract<LogEntry, { readonly _tag: 'agent-finished' }> =>
-	entry._tag === 'agent-finished'
+	Predicate.isTagged(entry, 'agent-finished')
 
 type ModelCarrier = Extract<LogEntry, { readonly _tag: 'agent_started' | 'model-change' }>
 const carriesModel = (entry: LogEntry): entry is ModelCarrier =>
-	entry._tag === 'agent_started' || entry._tag === 'model-change'
+	Predicate.isTagged(entry, 'agent_started') || Predicate.isTagged(entry, 'model-change')
 
 type FinishedAssistantMessage = Extract<LogEntry, { readonly _tag: 'assistant-message' }> & {
 	readonly finish: NonNullable<Extract<LogEntry, { readonly _tag: 'assistant-message' }>['finish']>
 }
 const isFinishedAssistantMessage = (entry: LogEntry): entry is FinishedAssistantMessage =>
-	entry._tag === 'assistant-message' && entry.finish !== null
+	Predicate.isTagged(entry, 'assistant-message') && entry.finish !== null
 
 const userMessageText = (entry: Extract<LogEntry, { readonly _tag: 'user-message' }>): string => {
 	const content = entry.message.content
@@ -233,7 +233,8 @@ const computeStatus = (
 ): SessionSummary['status'] => {
 	// No finish yet, or activity after the last finish → derive from latest activity
 	if (lastFinished === undefined || (latestRootEntry !== undefined && latestRootEntry.seq > lastFinished.seq)) {
-		return latestRootEntry?._tag === 'system-message' || latestRootEntry?._tag === 'agent_started'
+		return Predicate.isTagged(latestRootEntry, 'system-message') ||
+			Predicate.isTagged(latestRootEntry, 'agent_started')
 			? 'ready'
 			: 'running'
 	}
@@ -306,7 +307,7 @@ const isCacheHit = (
 	ref: SessionLogRef,
 ): cached is typeof SummaryIndexRecord.Type =>
 	cached !== undefined &&
-	cached._tag === 'summary' &&
+	Predicate.isTagged(cached, 'summary') &&
 	cached.sourceMtimeMs === ref.mtimeMs &&
 	cached.sourceSize === (ref.size ?? 0)
 
@@ -344,7 +345,11 @@ export const listSessionSummaries = (options?: SessionLayoutOptions): Effect.Eff
 						summary === null
 							? Effect.void
 							: appendSessionIndexRecord(
-									{ _tag: 'summary', sourceMtimeMs: ref.mtimeMs, sourceSize: ref.size ?? 0, summary },
+									SummaryIndexRecord.make({
+										sourceMtimeMs: ref.mtimeMs,
+										sourceSize: ref.size ?? 0,
+										summary,
+									}),
 									options,
 								),
 					),
@@ -376,7 +381,7 @@ export const deleteSession = (
 		const outputExists = yield* fs.exists(outputDirectory).pipe(Effect.orDie)
 		yield* fs.remove(logPath).pipe(Effect.orDie)
 		const ts = yield* Clock.currentTimeMillis
-		yield* appendSessionIndexRecord({ _tag: 'deleted', sessionId, ts }, options)
+		yield* appendSessionIndexRecord(DeletedIndexRecord.make({ sessionId, ts }), options)
 		if (!outputExists) return { deleted: true, outputRemoved: true }
 
 		const outputRemoval = yield* Effect.exit(fs.remove(outputDirectory, { recursive: true }))
@@ -417,12 +422,11 @@ export const refreshSessionSummaryIndex = (sessionId: SessionId, options?: Sessi
 					summary === null
 						? Effect.void
 						: appendSessionIndexRecord(
-								{
-									_tag: 'summary',
+								SummaryIndexRecord.make({
 									sourceMtimeMs: ref.mtimeMs,
 									sourceSize: ref.size ?? 0,
 									summary,
-								},
+								}),
 								options,
 							),
 				),

packages/fold-agent/src/Session/TitleGenerator.ts

@@ -1,6 +1,6 @@
 import type { LogEntry, FoldModel } from '@humanlayer/fold-core'
 import { languageModelLayerFor } from '@humanlayer/fold-core'
-import { Effect, Schema } from 'effect'
+import { Predicate, Effect, Schema } from 'effect'
 import { LanguageModel } from 'effect/unstable/ai'
 
 const TitleResult = Schema.Struct({ title: Schema.String })
@@ -9,7 +9,7 @@ const MAX_TRANSCRIPT_CHARS = 12_000
 type MessageEntry = Extract<LogEntry, { readonly _tag: 'user-message' | 'assistant-message' }>
 
 const isMessageEntry = (entry: LogEntry): entry is MessageEntry =>
-	entry._tag === 'user-message' || entry._tag === 'assistant-message'
+	Predicate.isTagged(entry, 'user-message') || Predicate.isTagged(entry, 'assistant-message')
 
 const extractMessageText = (entry: MessageEntry): string =>
 	typeof entry.message.content === 'string'
@@ -30,7 +30,7 @@ export const normalizeSessionTitle = (title: string): string =>
 		.join(' ')
 
 export const fallbackSessionTitle = (entries: ReadonlyArray<LogEntry>, rootAgentId: string): string => {
-	const first = entries.find((entry) => entry._tag === 'user-message' && entry.agentId === rootAgentId)
+	const first = entries.find((entry) => Predicate.isTagged(entry, 'user-message') && entry.agentId === rootAgentId)
 	return normalizeSessionTitle(first === undefined ? '' : messageText(first)) || 'Untitled session'
 }
 
@@ -39,9 +39,10 @@ export const titleTranscript = (entries: ReadonlyArray<LogEntry>, rootAgentId: s
 	entries
 		.filter(
 			(entry) =>
-				entry.agentId === rootAgentId && (entry._tag === 'user-message' || entry._tag === 'assistant-message'),
+				entry.agentId === rootAgentId &&
+				(Predicate.isTagged(entry, 'user-message') || Predicate.isTagged(entry, 'assistant-message')),
 		)
-		.map((entry) => `${entry._tag === 'user-message' ? 'User' : 'Assistant'}: ${messageText(entry)}`)
+		.map((entry) => `${Predicate.isTagged(entry, 'user-message') ? 'User' : 'Assistant'}: ${messageText(entry)}`)
 		.join('\n')
 		.slice(0, MAX_TRANSCRIPT_CHARS)