feat(tui): improve session fork handling

packages/core/src/database/migration.gen.ts

@@ -46,5 +46,6 @@ export const migrations = (
     import("./migration/20260703190000_reset_v2_shell_event_payloads"),
     import("./migration/20260703200000_reset_v2_session_events"),
     import("./migration/20260705180000_rename_instructions"),
+    import("./migration/20260706223930_add-session-fork"),
   ])
 ).map((module) => module.default) satisfies DatabaseMigration.Migration[]

packages/core/src/database/migration/20260706223930_add-session-fork.ts

@@ -0,0 +1,39 @@
+import { Effect } from "effect"
+import type { DatabaseMigration } from "../migration"
+
+export default {
+  id: "20260706223930_add-session-fork",
+  up(tx) {
+    return Effect.gen(function* () {
+      yield* tx.run(`ALTER TABLE \`session\` ADD \`fork_session_id\` text;`)
+      yield* tx.run(`ALTER TABLE \`session\` ADD \`fork_message_id\` text;`)
+      yield* tx.run(`
+        UPDATE \`session\`
+        SET
+          \`parent_id\` = NULL,
+          \`fork_session_id\` = (
+            SELECT json_extract(\`event\`.\`data\`, '$.parentID')
+            FROM \`event\`
+            WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+              AND \`event\`.\`type\` = 'session.forked'
+            ORDER BY \`event\`.\`seq\`
+            LIMIT 1
+          ),
+          \`fork_message_id\` = (
+            SELECT json_extract(\`event\`.\`data\`, '$.from')
+            FROM \`event\`
+            WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+              AND \`event\`.\`type\` = 'session.forked'
+            ORDER BY \`event\`.\`seq\`
+            LIMIT 1
+          )
+        WHERE EXISTS (
+          SELECT 1
+          FROM \`event\`
+          WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+            AND \`event\`.\`type\` = 'session.forked'
+        );
+      `)
+    })
+  },
+} satisfies DatabaseMigration.Migration

packages/core/src/database/schema.gen.ts

@@ -196,6 +196,8 @@ export default {
           \`project_id\` text NOT NULL,
           \`workspace_id\` text,
           \`parent_id\` text,
+          \`fork_session_id\` text,
+          \`fork_message_id\` text,
           \`slug\` text NOT NULL,
           \`directory\` text NOT NULL,
           \`path\` text,

packages/core/src/session.ts

@@ -746,6 +746,7 @@ const materializeAttachment = Effect.fn("V2Session.materializeAttachment")(funct
         start: undefined,
         end: undefined,
         name: undefined,
+        mime: undefined,
       }
     : yield* readFileAttachment(fs, input.uri)
   if (resolved.bytes.byteLength > MAX_ATTACHMENT_BYTES)
@@ -754,7 +755,7 @@ const materializeAttachment = Effect.fn("V2Session.materializeAttachment")(funct
       message: `Attachment exceeds the ${MAX_ATTACHMENT_BYTES} byte limit: ${input.uri}`,
     })
 
-  const mime = Mime.detect(resolved.bytes)
+  const mime = resolved.mime ?? Mime.detect(resolved.bytes)
   const content =
     mime === "text/plain" && resolved.start !== undefined
       ? Buffer.from(
@@ -791,6 +792,25 @@ const readFileAttachment = Effect.fn("V2Session.readFileAttachment")(function* (
   const info = yield* fs.stat(target).pipe(
     Effect.mapError(() => new AttachmentError({ uri, message: `Unable to read attachment: ${uri}` })),
   )
+  if (info.type === "Directory") {
+    const entries = yield* fs.readDirectoryEntries(target).pipe(
+      Effect.mapError(() => new AttachmentError({ uri, message: `Unable to read attachment: ${uri}` })),
+    )
+    return {
+      bytes: Buffer.from(
+        entries
+          .filter((entry) => entry.type === "file" || entry.type === "directory")
+          .sort((a, b) => (a.type === b.type ? a.name.localeCompare(b.name) : a.type === "directory" ? -1 : 1))
+          .map((entry) => entry.name + (entry.type === "directory" ? path.sep : ""))
+          .join("\n"),
+      ),
+      source: { type: "uri" as const, uri },
+      start: undefined,
+      end: undefined,
+      name: path.basename(target),
+      mime: "application/x-directory",
+    }
+  }
   if (info.type !== "File") return yield* new AttachmentError({ uri, message: `Attachment is not a file: ${uri}` })
   if (Number(info.size) > MAX_ATTACHMENT_BYTES)
     return yield* new AttachmentError({
@@ -800,7 +820,7 @@ const readFileAttachment = Effect.fn("V2Session.readFileAttachment")(function* (
   const bytes = yield* fs.readFile(target).pipe(
     Effect.mapError(() => new AttachmentError({ uri, message: `Unable to read attachment: ${uri}` })),
   )
-  return { bytes, source: { type: "uri" as const, uri }, start, end, name: path.basename(target) }
+  return { bytes, source: { type: "uri" as const, uri }, start, end, name: path.basename(target), mime: undefined }
 })
 
 function decodeDataURL(uri: string) {

packages/core/src/session/info.ts

@@ -17,6 +17,12 @@ export function fromRow(row: typeof SessionTable.$inferSelect): SessionSchema.In
     projectID: ProjectV2.ID.make(row.project_id),
     title: row.title,
     parentID: row.parent_id ? SessionSchema.ID.make(row.parent_id) : undefined,
+    fork: row.fork_session_id
+      ? {
+          sessionID: SessionSchema.ID.make(row.fork_session_id),
+          messageID: row.fork_message_id ? SessionMessage.ID.make(row.fork_message_id) : undefined,
+        }
+      : undefined,
     agent: row.agent ? AgentV2.ID.make(row.agent) : undefined,
     model: row.model
       ? {

packages/core/src/session/projector.ts

@@ -190,7 +190,9 @@ const projectFork = Effect.fn("SessionProjector.projectFork")(function* (
     .insert(SessionTable)
     .values({
       id: event.data.sessionID,
-      parent_id: event.data.parentID,
+      parent_id: null,
+      fork_session_id: event.data.parentID,
+      fork_message_id: event.data.from,
       project_id: parent.project_id,
       workspace_id: parent.workspace_id,
       slug: Slug.create(),

packages/core/src/session/runner/to-llm-message.ts

@@ -41,6 +41,26 @@ const textAttachment = (file: FileAttachment) =>
     },
   })
 
+const directoryAttachment = (file: FileAttachment) =>
+  Message.make({
+    role: "user",
+    content: [
+      `Attached directory: ${file.name ?? (file.source.type === "uri" ? file.source.uri : "directory")}`,
+      file.description === undefined ? undefined : `Description: ${file.description}`,
+      file.data.length === 0 ? undefined : "",
+      file.data.length === 0 ? undefined : Buffer.from(file.data, "base64").toString("utf8"),
+    ]
+      .filter((line): line is string => line !== undefined)
+      .join("\n"),
+    metadata: {
+      attachment: {
+        source: file.source,
+        name: file.name,
+        description: file.description,
+      },
+    },
+  })
+
 const decodeToolInput = Schema.decodeUnknownOption(Schema.UnknownFromJsonString)
 
 const providerMetadata = (
@@ -157,6 +177,7 @@ function toLLMMessage(message: SessionMessage.Message, model: ModelV2.Ref): Mess
       const files = message.files ?? []
       return [
         ...files.filter((file) => file.mime === "text/plain").map(textAttachment),
+        ...files.filter((file) => file.mime === "application/x-directory").map(directoryAttachment),
         Message.make({
           id: message.id,
           role: "user",

packages/core/src/session/sql.ts

@@ -29,6 +29,8 @@ export const SessionTable = sqliteTable(
       .references(() => ProjectTable.id, { onDelete: "cascade" }),
     workspace_id: text().$type<WorkspaceV2.ID>(),
     parent_id: text().$type<SessionSchema.ID>(),
+    fork_session_id: text().$type<SessionSchema.ID>(),
+    fork_message_id: text().$type<SessionMessage.ID>(),
     slug: text().notNull(),
     directory: directoryColumn().notNull(),
     path: pathColumn(),