fix: remove avoidable model runtime limits

Preserve long histories and parsed attachments, expose paged process and Subagent output, isolate MCP discovery failures, and expand browser snapshots and knowledge result selection. Remove fixed Harness output and updated remote Runtime duration limits.

Keep released Agent profile and v1 bridge compatibility while enabling larger framed exchanges and optional limits for updated peers. Document remote coverage requirements and real-model boundary validation.

Release note: Long model tasks can retain more context and continue reading complete tool output; remote execution preserves compatibility with released Agents. Updated remote limits require an updated Agent and Runtime bundle.

src/shared/assistant-contracts.ts

@@ -207,14 +207,14 @@ export const conversationMessageBlockSchema = z.discriminatedUnion('type', [
     .object({
       id: assistantIdSchema,
       type: z.literal('text'),
-      content: z.string().min(1).max(1_000_000)
+      content: z.string().min(1)
     })
     .strict(),
   z
     .object({
       id: assistantIdSchema,
       type: z.literal('reasoning'),
-      content: z.string().min(1).max(1_000_000)
+      content: z.string().min(1)
     })
     .strict(),
   z
@@ -314,7 +314,7 @@ export const conversationMessageSchema = z
     id: assistantIdSchema,
     queueItemId: assistantIdSchema.optional(),
     role: z.enum(['user', 'assistant']),
-    content: z.string().max(1_000_000),
+    content: z.string(),
     reasoning: z.string().optional(),
     blocks: conversationMessageBlocksSchema.optional(),
     displayCaptureTruncated: z.boolean().optional(),
@@ -402,17 +402,12 @@ export type ConversationMessage = z.infer<
   typeof conversationMessageSchema
 >
 
-export const maximumConversationHistoryMessages = 500
-export const maximumConversationHistoryCharacters = 2_000_000
 export const conversationHistoryMessageSchema =
   conversationMessageSchema
     .pick({
       role: true,
       content: true
     })
-    .extend({
-      content: z.string().max(100_000)
-    })
     .strict()
 
 export const conversationContextMetricsSchema = z
@@ -452,7 +447,7 @@ export type ConversationContextMetrics = z.infer<
 export const conversationContextCompressionStateSchema = z
   .object({
     coveredHistoryDigest: z.string().regex(/^[0-9a-f]{64}$/u),
-    coveredMessageCount: z.number().int().nonnegative().max(500),
+    coveredMessageCount: z.number().int().nonnegative(),
     coveredFromMessageId: assistantIdSchema.optional(),
     coveredThroughMessageId: assistantIdSchema.optional(),
     summary: z.string().trim().min(1).max(100_000)
@@ -502,9 +497,7 @@ export const conversationSnapshotSchema = z
     branch: conversationBranchSchema.optional(),
     title: z.string().trim().min(1).max(200),
     updatedAt: z.number().int().nonnegative(),
-    messages: z
-      .array(conversationMessageSchema)
-      .max(500)
+    messages: z.array(conversationMessageSchema)
   })
   .strict()
 
@@ -528,7 +521,7 @@ export type LocalConversationHeader = z.infer<
 export const localConversationSaveSchema = z
   .object({
     header: localConversationHeaderSchema,
-    messages: z.array(conversationMessageSchema).max(500)
+    messages: z.array(conversationMessageSchema)
   })
   .strict()