fix(wand): stop markdown code fences landing in generated code by waleedlatif1 · Pull Request #6289 · simstudioai/sim

waleedlatif1 · 2026-08-05T17:21:33Z

Summary

Strip markdown code fences from wand output for raw-value generation types. Only applies when the response opens with a fence, so code that merely contains a backtick run in a template literal or docstring is never touched
Reset the wand conversation history when a Function block switches language. maintainHistory was replaying the previous language's assistant turn, which kept steering generations back to it
Feed the sanitized text into history so one fenced reply can't become the in-context example for every later turn
Give PYTHON_AI_PROMPT the worked example the JavaScript prompt already had, and align its import rule with the sandbox package list
Reinforce the no-markdown instruction server-side for javascript-function-body, matching what cron-expression and json-object already do

Two known non-goals: a response that starts with prose before the fence, and mid-stream display (the editor may briefly show a fence before the final value replaces it). Both are deliberate — per-chunk stripping would mean guessing whether a trailing backtick run opens a fence or is part of the code.

Type of Change

Bug fix

Testing

15 unit tests on the sanitizer covering full wrap, missing closing fence, untagged fence, indentation preservation, multi-fence, idempotence, and the must-not-touch cases. Verified the tests fail when the util is stubbed out. Full suite green (18,597 passing), typecheck, biome, and check:api-validation all clean.

Checklist

Code follows project style guidelines
Self-reviewed my changes
Tests added/updated and passing
No new warnings introduced
I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

vercel · 2026-08-05T17:21:40Z

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cursor · 2026-08-05T17:21:54Z

PR Summary

Medium Risk
Changes wand output handling and multi-turn history for workflow code generation; logic is guarded by generation type and covered by unit tests, but incorrect stripping could still corrupt user code in edge cases.

Overview
Fixes wand (AI code generation) so markdown fences and stale chat history no longer corrupt function bodies and other raw-value outputs.

Fence stripping: New stripCodeFences / shouldStripCodeFences run after the stream completes for machine-value generation types (function bodies, JSON, cron, SQL, etc.), not free-form system-prompt. Stripping only when the response opens with a fence avoids breaking code that legitimately contains backticks in template literals or docstrings. Sanitized text is what gets written to the editor and stored in wand history so one fenced reply cannot anchor later turns.

History reset: useWand accepts historyResetKey (the Function block passes language). Changing it clears conversation history and uses an epoch so in-flight requests from the old context cannot append after a reset—fixing generations that kept reverting to the previous language when maintainHistory was on.

Prompts: The wand API adds server-side “raw function body only, no markdown” reinforcement for javascript-function-body. The Python AI prompt gains sandbox-aware import rules, a worked example, and explicit “no prose” output rules aligned with JavaScript.

Removed: onGenerationComplete from useWand (unused after sanitization moved into the hook).

^{Reviewed by Cursor Bugbot for commit 68e1192. Configure here.}

greptile-apps · 2026-08-05T17:24:36Z

Greptile Summary

The PR sanitizes markdown-fenced Wand responses, resets generation history when Function blocks switch languages, and strengthens raw-code prompting.

Adds final-response fence stripping for machine-readable generation types.
Prevents retired language contexts from being appended to conversation history.
Expands the Python generation prompt and reinforces raw function-body output server-side.

Confidence Score: 4/5

The PR does not appear safe to merge until the outstanding sanitizer path that removes a valid trailing embedded fence is resolved.

The current sanitizer still unconditionally removes a final fence-like line, so a response truncated immediately after a delimiter embedded in generated code is persisted in corrupted form.

Files Needing Attention: apps/sim/lib/wand/strip-code-fences.ts and apps/sim/lib/wand/strip-code-fences.test.ts

Important Files Changed

Filename	Overview
apps/sim/lib/wand/strip-code-fences.ts	Introduces conservative outer-fence removal while retaining the previously reported corruption when a truncated embedded delimiter is the final line.
apps/sim/lib/wand/strip-code-fences.test.ts	Covers wrapped, truncated, nested, multi-block, and untouched output cases, including the acknowledged trailing-delimiter behavior.
apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-wand.ts	Sanitizes completed output and uses an epoch guard to keep retired language turns out of conversation history.
apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/code/code.tsx	Keys Wand history resets to Function block language changes and expands Python generation guidance.
apps/sim/app/api/wand/route.ts	Adds language-neutral server-side instructions requiring raw function-body output.

_{Reviews (6): Last reviewed commit: "test(wand): record the trailing-fence am..." | Re-trigger Greptile}

waleedlatif1 · 2026-08-05T17:44:40Z

@greptile

waleedlatif1 · 2026-08-05T17:44:44Z

@cursor review

Strip fences from wand output for raw-value generation types, reset the conversation history when a Function block switches language, and give the Python prompt the worked example the JavaScript one already had.

Slice only the outermost fence delimiters so a fenced body containing line-leading backticks keeps every interior line, and skip the history append when a language reset retired the request mid-flight.

The trimStart check made the -1 branch dead and stated "opens with a fence" twice. Derive it once from the first fence line's position.

waleedlatif1 · 2026-08-05T17:54:30Z

@greptile

waleedlatif1 · 2026-08-05T17:54:31Z

@cursor review

cursor

✅ Bugbot reviewed your changes and found no new issues!

2 issues from previous reviews remain unresolved.

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit fb8337a. Configure here.}

No call site ever passed it, so the branch never ran. The props interface makes the removal compile-time verified.

waleedlatif1 · 2026-08-05T17:58:27Z

@greptile

waleedlatif1 · 2026-08-05T17:58:28Z

@cursor review

cursor

✅ Bugbot reviewed your changes and found no new issues!

2 issues from previous reviews remain unresolved.

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit c89adb2. Configure here.}

A truncated response whose body embeds line-leading backticks lost every line after the first embedded delimiter. Only the opening line and a final fence line are removed now. Sync the history epoch in a layout effect so a request settling before the passive flush cannot append to already-reset history.

waleedlatif1 · 2026-08-05T18:05:19Z

@greptile

waleedlatif1 · 2026-08-05T18:05:20Z

@cursor review

cursor

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 5985357. Configure here.}

A bare fence on the last line closes the wrapper in every well-formed response and is content only when generation stopped exactly on an embedded delimiter. Nothing separates the two, so assert the chosen behavior instead of leaving it implicit.

waleedlatif1 · 2026-08-05T18:11:01Z

@greptile

waleedlatif1 · 2026-08-05T18:11:02Z

@cursor review

cursor

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 68e1192. Configure here.}

greptile-apps Bot reviewed Aug 5, 2026

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Comment thread apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-wand.ts Outdated

Comment thread apps/sim/lib/wand/strip-code-fences.ts Outdated

Comment thread apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-wand.ts

waleedlatif1 force-pushed the fix/wand-markdown-code-fences branch from 3742f1b to 2a70483 Compare August 5, 2026 17:44

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Comment thread apps/sim/lib/wand/strip-code-fences.ts Outdated

Comment thread apps/sim/app/workspace/[workspaceId]/w/[workflowId]/hooks/use-wand.ts

waleedlatif1 added 3 commits August 5, 2026 10:54

fix(wand): stop markdown code fences landing in generated code

fe0cd6a

Strip fences from wand output for raw-value generation types, reset the conversation history when a Function block switches language, and give the Python prompt the worked example the JavaScript one already had.

fix(wand): preserve nested fences and retire stale history on reset

4e7dfb0

Slice only the outermost fence delimiters so a fenced body containing line-leading backticks keeps every interior line, and skip the history append when a language reset retired the request mid-flight.

refactor(wand): drop unreachable guard in fence stripper

fb8337a

The trimStart check made the -1 branch dead and stated "opens with a fence" twice. Derive it once from the first fence line's position.

waleedlatif1 force-pushed the fix/wand-markdown-code-fences branch from 2a70483 to fb8337a Compare August 5, 2026 17:54

vercel Bot temporarily deployed to Preview August 5, 2026 17:54 Inactive

greptile-apps Bot reviewed Aug 5, 2026

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Comment thread apps/sim/lib/wand/strip-code-fences.ts Outdated

cursor Bot reviewed Aug 5, 2026

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chore(wand): remove unused onGenerationComplete callback

c89adb2

No call site ever passed it, so the branch never ran. The props interface makes the removal compile-time verified.

vercel Bot temporarily deployed to Preview August 5, 2026 17:58 Inactive

cursor Bot reviewed Aug 5, 2026

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vercel Bot temporarily deployed to Preview August 5, 2026 18:05 Inactive

cursor Bot reviewed Aug 5, 2026

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greptile-apps Bot reviewed Aug 5, 2026

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Comment thread apps/sim/lib/wand/strip-code-fences.ts Outdated

vercel Bot temporarily deployed to Preview August 5, 2026 18:11 Inactive

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waleedlatif1 merged commit 2d90c72 into staging Aug 5, 2026
30 checks passed

waleedlatif1 deleted the fix/wand-markdown-code-fences branch August 5, 2026 18:29

waleedlatif1 mentioned this pull request Aug 5, 2026

v0.7.57: forking webhook URL, markdown editor overflow, fix ui improvements #6287

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Summary

Type of Change

Testing

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Confidence Score: 4/5

Important Files Changed

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