sshiv012 opened a new pull request, #6211:
URL: https://github.com/apache/texera/pull/6211
### What changes were proposed in this PR?
The Texera AI agent edits the user's **live workflow canvas**, its tools
add, modify, and delete operators, and the changes auto-persist. Until now
there was no agent-aware way to back out a turn that went wrong; the user had
to manually undo a multi-operator change. This PR adds two controls:
- **Per-turn "Revert"** rewinds the workflow (and the agent-service's
`HEAD`) to the state
*before* an agent turn.
- **"Redo"** undoes the most recent revert; a redo stack supports multiple
consecutive
reverts→redos, and is cleared when a new prompt starts a new branch.
**Use case / why:** the agent mutates real state, so a bad suggestion (a
wrong delete, an unwanted restructure) is expensive to recover from. A cheap,
reliable "step back" lowers the cost of letting the agent experiment. A
frontend-only visual undo is insufficient, the agent-service keeps its own
`HEAD`, so the next message would silently clobber a cosmetic revert. This does
a **true rewind** that keeps the agent's context consistent.
**How it works:** the agent-service already models a conversation as a
version tree of ReAct steps (`id`/`parentId` +
`beforeWorkflowContent`/`afterWorkflowContent` snapshots + a `HEAD` pointer).
The only missing primitive was moving `HEAD` backward.
- *Revert(T):* `HEAD ← parent(T)`, restore `T.beforeWorkflowContent`, push
old HEAD onto an in-memory redo stack (reverted steps stay in the tree, nothing
is deleted).
- *Redo:* pop the stack, move `HEAD` forward, restore that step's
`afterWorkflowContent`.
- A new prompt / clear-history clears the redo stack.
- Both commands are rejected while the agent is `GENERATING`, to avoid
racing the loop's own HEAD/workflow mutations.
**Protocol additions:** `WsClientRevertCommand { messageId }`,
`WsClientRedoCommand` (client→server); `WsServerHeadChangeEvent { headId,
workflowContent, canRedo }` and a `canRedo` field on `WsServerSnapshotEvent`
(server→client, so a reconnecting client renders the correct Redo state).
No new persistence, no schema changes, no new services; revert/redo state is
the in-memory step tree the agent already maintains.
*Scoped as follow-ups:* per-individual-step revert, forward/branch
navigation UI beyond single-level redo, and persisting revert history across
agent-service restarts (currently session-scoped).
### Any related issues, documentation, discussions?
Design discussion / RFC: apache/texera#6039
### How was this PR tested?
New automated tests were added and all existing suites pass:
- **agent-service (bun):** unit tests for `revertToTurnStart` / `redo` /
`canRedo`, clear-on-new-prompt, and the WS command handlers including
reject-while-generating, unknown-turn, and nothing-to-redo negative cases.
- **frontend (vitest):** the `WsServerHeadChangeEvent` handler (HEAD update
+ `canRedo` + canvas reload), the `revertTurn` / `redo` senders, and the button
enable/disable logic.
Full local run of the CI pipeline for both services (rebased on latest
`main`) passes: `format` / `typecheck` / `bun test` (agent-service), and
`format:ci` / `build:ci` / `test:ci` / browser-mode tests (frontend).
Manual: agent adds operators → **Revert** rolls them back → **Redo**
restores them → sending a new message branches and clears Redo.
### Was this PR authored or co-authored using generative AI tooling?
Generated-by: Claude Code (Claude Opus 4.8)
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