refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/src/session/revert.ts

@@ -0,0 +1,138 @@
+import z from "zod"
+import { SessionID, MessageID, PartID } from "./schema"
+import { Snapshot } from "../snapshot"
+import { MessageV2 } from "./message-v2"
+import { Session } from "."
+import { Log } from "../util/log"
+import { Database, eq } from "../storage/db"
+import { MessageTable, PartTable } from "./session.sql"
+import { Storage } from "@/storage/storage"
+import { Bus } from "../bus"
+import { SessionPrompt } from "./prompt"
+import { SessionSummary } from "./summary"
+
+export namespace SessionRevert {
+  const log = Log.create({ service: "session.revert" })
+
+  export const RevertInput = z.object({
+    sessionID: SessionID.zod,
+    messageID: MessageID.zod,
+    partID: PartID.zod.optional(),
+  })
+  export type RevertInput = z.infer<typeof RevertInput>
+
+  export async function revert(input: RevertInput) {
+    SessionPrompt.assertNotBusy(input.sessionID)
+    const all = await Session.messages({ sessionID: input.sessionID })
+    let lastUser: MessageV2.User | undefined
+    const session = await Session.get(input.sessionID)
+
+    let revert: Session.Info["revert"]
+    const patches: Snapshot.Patch[] = []
+    for (const msg of all) {
+      if (msg.info.role === "user") lastUser = msg.info
+      const remaining = []
+      for (const part of msg.parts) {
+        if (revert) {
+          if (part.type === "patch") {
+            patches.push(part)
+          }
+          continue
+        }
+
+        if (!revert) {
+          if ((msg.info.id === input.messageID && !input.partID) || part.id === input.partID) {
+            // if no useful parts left in message, same as reverting whole message
+            const partID = remaining.some((item) => ["text", "tool"].includes(item.type)) ? input.partID : undefined
+            revert = {
+              messageID: !partID && lastUser ? lastUser.id : msg.info.id,
+              partID,
+            }
+          }
+          remaining.push(part)
+        }
+      }
+    }
+
+    if (revert) {
+      const session = await Session.get(input.sessionID)
+      revert.snapshot = session.revert?.snapshot ?? (await Snapshot.track())
+      await Snapshot.revert(patches)
+      if (revert.snapshot) revert.diff = await Snapshot.diff(revert.snapshot)
+      const rangeMessages = all.filter((msg) => msg.info.id >= revert!.messageID)
+      const diffs = await SessionSummary.computeDiff({ messages: rangeMessages })
+      await Storage.write(["session_diff", input.sessionID], diffs)
+      Bus.publish(Session.Event.Diff, {
+        sessionID: input.sessionID,
+        diff: diffs,
+      })
+      return Session.setRevert({
+        sessionID: input.sessionID,
+        revert,
+        summary: {
+          additions: diffs.reduce((sum, x) => sum + x.additions, 0),
+          deletions: diffs.reduce((sum, x) => sum + x.deletions, 0),
+          files: diffs.length,
+        },
+      })
+    }
+    return session
+  }
+
+  export async function unrevert(input: { sessionID: SessionID }) {
+    log.info("unreverting", input)
+    SessionPrompt.assertNotBusy(input.sessionID)
+    const session = await Session.get(input.sessionID)
+    if (!session.revert) return session
+    if (session.revert.snapshot) await Snapshot.restore(session.revert.snapshot)
+    return Session.clearRevert(input.sessionID)
+  }
+
+  export async function cleanup(session: Session.Info) {
+    if (!session.revert) return
+    const sessionID = session.id
+    const msgs = await Session.messages({ sessionID })
+    const messageID = session.revert.messageID
+    const preserve = [] as MessageV2.WithParts[]
+    const remove = [] as MessageV2.WithParts[]
+    let target: MessageV2.WithParts | undefined
+    for (const msg of msgs) {
+      if (msg.info.id < messageID) {
+        preserve.push(msg)
+        continue
+      }
+      if (msg.info.id > messageID) {
+        remove.push(msg)
+        continue
+      }
+      if (session.revert.partID) {
+        preserve.push(msg)
+        target = msg
+        continue
+      }
+      remove.push(msg)
+    }
+    for (const msg of remove) {
+      Database.use((db) => db.delete(MessageTable).where(eq(MessageTable.id, msg.info.id)).run())
+      await Bus.publish(MessageV2.Event.Removed, { sessionID: sessionID, messageID: msg.info.id })
+    }
+    if (session.revert.partID && target) {
+      const partID = session.revert.partID
+      const removeStart = target.parts.findIndex((part) => part.id === partID)
+      if (removeStart >= 0) {
+        const preserveParts = target.parts.slice(0, removeStart)
+        const removeParts = target.parts.slice(removeStart)
+        target.parts = preserveParts
+        for (const part of removeParts) {
+          Database.use((db) => db.delete(PartTable).where(eq(PartTable.id, part.id)).run())
+          await Bus.publish(MessageV2.Event.PartRemoved, {
+            sessionID: sessionID,
+            messageID: target.info.id,
+            partID: part.id,
+          })
+        }
+      }
+    }
+    await Session.clearRevert(sessionID)
+  }
+}