Fix blank code blocks in assistant - #5772

Keep cancellable work in the task body

When the inputs change after getSource resolves but while ApplySearchReplaceBlockTool.execute() is awaiting its module load, cancelling this restartable task stops only the outer task at this await; loadDiff() is a separate ordinary async operation, and the abort signal no longer stops it after the fetch. The superseded operation can therefore later overwrite originalCode, modifiedCode, or errorMessage belonging to the newer patch (and can also mutate after destruction), displaying or copying a stale diff. Keep the state-mutating awaits directly in the task or verify the controller/signal after every await before assigning resource state.

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[Claude Code 🤖] Real bug, and precisely diagnosed. Fixed in f3d3f89.

You're right about the boundary: loadDiff is an ordinary async function, so cancelling the task only stops things at the await inside the task body. Past that, the abort signal reaches the fetch and nothing else — ApplySearchReplaceBlockTool.execute() awaits a module load with no knowledge of it.

Worth naming the exact hole, because it wasn't where I'd assumed. The catch after getSource already had if (signal.aborted) return, so I'd covered the fetch rejected mid-flight case. What was uncovered was the success path — a fetch that completed before the supersession, followed by an execute() that spans it. That run then resumed and assigned originalCode, modifiedCode, and errorMessage belonging to the newer patch.

Took the second of your two options — verify after every await — rather than moving the work into the task body, because it holds regardless of how ember-concurrency cancels an async task, and I didn't want the correctness of this to rest on my reading of those internals.

let result = await this.cardService.getSource(new URL(fileUrl), { signal });
if (signal.aborted) return;
originalCode = result.status === 404 ? '' : result.content;

…and the same guard on both the resolve and reject paths of execute(). One related change your comment implies: the patch is now applied against originalCode — the value this load fetched — instead of this.originalCode, which by then may belong to a different patch entirely.

The destruction case you mention falls out of the same guard, since the destructor aborts the controller.

Added a regression test that forces the ordering deterministically: two loads started with a deferred getSource, the newer one released and allowed to render its diff, then the abandoned one released afterwards. It asserts the diff still shows the newer replacement. Against the previous code the late load overwrites it.

Not verified locally — Colima is down here, so CI is exercising it.

[Claude Code 🤖] This early return is correct today, and it is one line away from being an infinite invalidation loop. The thing that keeps it safe lives in a different file and is not written down anywhere.

Background — why reading tracked state here is different from reading it anywhere else. ember-modify-based-class-resource's manager builds the resource inside createCache(() => { …; instance.modify(positional, named); return instance }) (dist/core/class-based/manager.js). Everything consumed during that computation — including tracked state read inside modify — entangles with the cache. Dirty it and the next getValue re-runs modify. this.isDataLoaded reads the tracked originalCode and modifiedCode; this.errorMessage is tracked too. So this line entangles all three, and load writes all three.

That combination is safe here for one reason only: every path that reads them returns without writing. Data loaded → return. Error set → return. Load in flight → return. The only way through to load.perform() is with all three falsy, and every terminal state loadDiff can reach sets one of them.

Except one. loadDiff opens with if (codePatchStatus === 'applied'), which sets originalCode = null, modifiedCode = null, and returns — the one exit that leaves neither data nor an error. Reach modify in that state with unchanged inputs and it goes: read isDataLoaded (false) → read errorMessage (null) → load.perform(). Ember-concurrency starts a task instance synchronously on perform, and loadDiff's applied branch has no await before its return, so those two writes land inside the same cache computation that just read them. In a debug build that is the backtracking assertion; in production it is the cache invalidating itself on every read.

Why it doesn't fire today. I traced every consumer of this resource before writing the above. There are exactly two, both in aibot-message.gts, and both exclude applied:

• codePatchErrorMessage returns null at its first branch when the status is applied, before it touches this.codeDiffResource.
• The template reads codeDiffResource.isDataLoaded / isLoadingDiff only inside the {{else}} of {{#if this.isAppliedOrIgnoredCodePatch}}, and that getter is codePatchStatus === 'applied' || !isLastAssistantMessage.

So modify is never called while the status is applied, the branch at loadDiff's top is unreachable from here, and the loop cannot start. That is a real invariant, held entirely by two guards in a component two files away, with nothing in this file recording it.

The fix is one clause, and it also makes the dead branch in loadDiff honest:

With that, applied is a terminal state of modify rather than a state load is asked to reach and then abandon, and the guard stops depending on a consumer's branch structure. The codePatchStatus === 'applied' block in loadDiff can then either go or stay as documentation — but it should not be the thing standing between this and a loop.

Scope. Latent, not live — nothing in the current app reaches it. Non-blocking, but it costs four tokens to remove and the failure mode if someone later renders a loading state for an applied patch is a render loop, not a wrong pixel.

[Claude Code 🤖] Taken, in ba5f454 — and the trace is right down to the synchronous write, which is the part that makes it a loop rather than a stale read.

I confirmed the reachability argument independently before changing anything: codePatchErrorMessage returns null at its first branch on applied, before touching the resource, and the template reads isDataLoaded / isLoadingDiff only inside the {{else}} of isAppliedOrIgnoredCodePatch. Resources are pull-based, so with no consumer reading it while applied, modify doesn't run and the branch is unreachable. Latent, as you say.

Worth naming the shape precisely, because it needs two calls: the first with applied has appliedStateChanged true, so it takes the inputsChanged branch and never reads the tracked state. It's the second call — same status, inputs unchanged — that reads all three, finds them falsy because the first load nulled them, and performs. That's the read-then-write inside one computation.

I ordered the new clause first rather than last:

if (
  codePatchStatus === 'applied' ||
  this.isDataLoaded ||
  this.errorMessage ||
  this.loadInFlight
) {

|| is left-to-right, so this returns without reading tracked state at all in the applied case — the entanglement never forms, instead of forming and then being harmless. Same four tokens.

I left the applied block at the top of loadDiff. With this change it's no longer load-bearing, but it's still reached on that first call and still does the nulling, so removing it would mean moving that clearing into modify — a bigger change than the problem justifies. It now reads as what it always claimed to be: documentation for why an applied patch has no diff to show.

[Claude Code 🤖] The comment states the right concern and then understates what the code does with it, which will mislead the next reader.

modify does consume tracked state, eight lines below: this.isDataLoaded reads the tracked originalCode and modifiedCode, and this.errorMessage is tracked. Both are written by load. So the resource is entangled with load state whether or not loadInFlight is tracked, and keeping this flag untracked buys something narrower than "we don't consume tracked state in modify" — it keeps a mid-flight signal out of the entanglement, so a load starting and finishing doesn't invalidate the cache twice on its own.

The invariant that actually makes the entanglement safe is worth writing down instead, because it is the one a future edit can break without noticing: every path in modify that reads isDataLoaded or errorMessage returns without writing them. Something like:

  // Untracked on purpose. `modify` runs inside the resource's tracked cache,
  // so anything it reads re-runs it when written. The load-completion state it
  // reads (`isDataLoaded`, `errorMessage`) is only ever read on paths that
  // return, so a completed load costs one extra `modify` and stops. A
  // mid-flight flag read the same way would add a second invalidation per
  // load, and a path that read either one and then started a load would
  // re-enter without bound.

Scope. Comment accuracy. Non-blocking — the code is right; the note next to it should describe the rule the code is following, since that rule is the whole safety argument. Related: the thread on the early return below, which is where that rule is closest to being broken.

[Claude Code 🤖] You're right, and the comment was worse than imprecise — it implied modify doesn't consume tracked state, when it does so eight lines below. Rewritten in ba5f454.

The version I landed states the invariant as the safety argument rather than as a property of the flag:

every path in modify that reads those returns without writing them, so a finished load costs one further modify and stops

with the narrower thing the untracked flag actually buys — sparing a second invalidation per load — kept as the secondary clause rather than the headline.

The pairing with the thread below is the useful part: that rule is what makes the entanglement safe, and the applied path was the one place it was about to be broken. Having fixed that, the comment now describes a rule the code actually keeps everywhere, which is the only kind worth writing down.

[Claude Code 🤖] The guard is right, and the same raw string still reaches an unguarded new URL one component away.

Confirmation on this getter. The fallback is the correct shape: new URL('malformed file url') throws, and 'malformed file url'.split('/').pop() gives back the whole string, which is what the model wrote and therefore the most useful thing to show. The test pins exactly that.

Where it doesn't reach. this.file (the @cached getter above) builds its FileDef with sourceUrl: this.sourceUrl ?? '', and sourceUrl returns this.args.codeData.fileUrl verbatim for a non-new file — the same unparseable string. That FileDef goes straight into <AttachedFileDropdownMenu @file={{this.file}} …>, whose openInCodeMode does new URL(this.args.file.sourceUrl!) (packages/host/app/components/ai-assistant/attached-file-dropdown-menu.gts). The '' case is reachable too: sourceUrl returns null for a new file that isn't applied yet, so this.file.sourceUrl is '' and new URL('') throws the same way.

That is a click-time throw inside an @action, not a render-time one, so it does not undo what this change fixes — the message renders, which was the point. But the menu item is offered on a header whose file URL this change has just established may not be a URL, and choosing it throws.

Scope. Follow-up, non-blocking, and arguably pre-existing rather than introduced here — the '' path predates this change. Worth either guarding openInCodeMode the same way, or omitting the "open in code mode" item when sourceUrl doesn't parse, so the header degrades consistently instead of half-way.

[Claude Code 🤖] The main finding holds and I'm treating it as a follow-up rather than folding it in — but one detail of it doesn't survive checking, and it's the half that would have decided the fix.

Confirmed: openInCodeMode does new URL(this.args.file.sourceUrl!) with no guard, and for a non-new file sourceUrl hands it codeData.fileUrl verbatim. So the unparseable-but-non-empty case — malformed file url, exactly what this change made renderable — is offered as an enabled menu item that throws on click.

Not confirmed: the '' case. The menu item carries disabled: !this.args.file?.sourceUrl (attached-file-dropdown-menu.gts), and '' is falsy, so the new-file-not-yet-applied path you describe is already disabled rather than reachable. That matters for the remedy: "omit the item when sourceUrl doesn't parse" is the right shape, but it's an extension of a guard that exists, not a missing guard — the existing one just tests presence where it needs to test parseability.

Why not here. It's a different component, a click-time throw rather than a render-time one, and the fix wants its own test around the menu rather than the header. This branch has had a long CI road and I'd rather not widen it for something no current path reaches on render. Happy to do it as a follow-up — disabled: !parses(this.args.file?.sourceUrl) with a small helper is the whole change.

Agreed on the framing though: this change established that a header's file URL may not be a URL, so anything downstream taking that string as one is now on notice.

[Claude Code 🤖] Non-blocking, two small things about this branch.

This {{#if}} is always true. isLoadingDiff requires this.load.isRunning, and modify performs the load only after if (!fileUrl) { this.errorMessage = 'Missing file URL in the code block'; return; }. So a running load implies a file URL, and the guard can go — one less branch to reason about in a template that already nests four deep. If it is here defensively, a comment saying so would keep the next reader from hunting for the case that needs it.

The state this branch exists to eliminate. Worth recording that it is now exhaustive, because that is the load-bearing property: after modify returns, the resource is always in exactly one of loaded (isDataLoaded), failed (errorMessage), or loading (load.isRunning) — the early return above only skips perform when one of the first two already holds, and every other path performs. The blank block this change removes was the fourth state, and there is no longer a way to reach it. That is the sentence I would want in the comment above rather than the rationale for the header, which is self-evident from the markup.

[Claude Code 🤖] Both taken in ba5f454.

The guard is gone. Your reasoning checks out: modify reaches load.perform() only past if (!fileUrl) { this.errorMessage = …; return; }, so a running load implies a file URL and isLoadingDiff requires load.isRunning. It wasn't defensive, just redundant — and one less branch in a template already nesting four deep is worth having. Nothing crashes if the invariant were ever broken either, since fileName now falls back rather than constructing a URL blindly.

The comment says the exhaustiveness now. That is the better content, and I'd missed that it was the point:

Together with the branch above, this makes the states a patch can be rendered in exhaustive: once modify returns, the resource holds code, or an error, or a running load. There is no fourth state, and the empty block this branch replaced was it.

The header rationale is down to one clause explaining why it can always name its file, which is the only part not evident from the markup.

Worth noting these two threads compose: with applied now returning from modify, "code, error, or running load" is exhaustive over every path modify can take, not just the ones a consumer currently reaches.

[Claude Code 🤖] Strong test — the fresh-CodeData-with-identical-values setup is the right reproduction, and I checked that it exercises what it claims: searchReplaceBlock is only populated once isCompleteSearchReplaceBlock passes (packages/host/app/lib/formatted-message/utils.ts), so after a block completes the same string arrives on every re-parse and this.searchReplaceBlock !== searchReplaceBlock is false by value comparison. The whole fix rests on that being a string rather than a rebuilt object, and this test would fail the moment it stopped being one.

The arm that isn't covered is the one from the other half of the report. The description names two symptoms: the block sat holding no code, and the error was cleared along with it. This test pins the success arm of the early return — isDataLoaded → don't refetch. The errorMessage arm has no equivalent, and it is the arm that governs a failing load: a file that 404s or a realm that errors must be fetched once and then left alone, with the message still on screen after N re-renders. Right now, deleting this.errorMessage from the early-return condition leaves every test in this file green while restoring a request-per-invalidation storm against exactly the URLs that were failing — which is the shape that took staging down.

It is a small addition on top of what is already here:

cardService.getSource = async () => {
  getSourceCallCount++;
  throw new Error('realm unavailable');
};
// …render, then re-render with identical parts N times…
assert.strictEqual(getSourceCallCount, 1, 'a failed load is not retried on every invalidation');
assert.dom('[data-test-error-message]').exists('and its message survives');

Scope. Test coverage, non-blocking — but this is the cheapest of the suggestions here and it guards the more expensive failure.

[Claude Code 🤖] Added in b888ce8 — you were right that this was the cheapest suggestion guarding the more expensive failure, so I did it first.

The test fetches once, fails, then re-renders five times with identical parts and asserts both halves: getSourceCallCount still 1, and [data-test-error-message] still on screen. Deleting this.errorMessage from the early-return condition now fails it, which was the gap — before this, that deletion was green.

Your point about why the existing test works is the part I'd want kept: searchReplaceBlock is a string populated only once isCompleteSearchReplaceBlock passes, so identical re-parses compare equal by value and fileOrPatchChanged stays false. The whole fix rests on that, and if it ever became a rebuilt object both tests would fail rather than silently stop testing anything — which is the right failure direction.

One caveat on the new test, stated plainly: it is typechecked and linted but unrun. Colima is down on this machine so the host suite can't start locally, and CI is the first thing to exercise it. Earlier in this branch's life two monaco-dependent tests passed review by reading and then failed on CI, so I've kept this one off the diff editor entirely — it asserts on the error alert and a call counter, nothing that depends on how monaco lays out panes.