[fix] Show short agent-run errors in full instead of clamping them away

[ashrafchowdury]

Context

When an agent run failed, the error reason in the chat could get cut off with no way to read the rest. The clamp and the "Show more" toggle used two different rules, so they could disagree: a short reason that happened to wrap past three lines got line-clamp-3, but the toggle only appeared for text over 220 chars or containing a newline. A wrapped-but-short message was clamped with no button to expand it, so part of the error was simply hidden (#5350). Multi-line reasons also lost their line breaks, since the default text block didn't preserve whitespace.

Changes

There's now one rule, isBigError, that decides everything:

const isBigError = (text) => text.length > 240 || text.split("\n").length > 4

• An everyday reason (short, ≤4 lines) renders in full, with whitespace-pre-wrap so its line breaks survive. No clamp, no toggle.
• A big reason (a stacktrace) clamps to three lines behind "Show more", which opens the scrollable <pre> block as before.

Because the clamp, the toggle, and the expanded view all key off the same isBigError check, they can't disagree and strand text off-screen.

Before:

• isLong = text.length > 220 || text.includes("\n") gated the toggle.
• line-clamp-3 was applied to every non-expanded reason regardless of isLong.
• Result: a short reason that wrapped past 3 lines was clamped with no expand button.

After:

• One isBigError check drives the clamp, the toggle, and the expanded block.
• Short reasons show fully (whitespace preserved); only big ones collapse behind "Show more".

Tests / notes

• Reviewers should check the two boundaries: a reason just under the 240-char / 4-line threshold (should show in full) and one just over it (should clamp with a working toggle).

What to QA

• Trigger an agent run that fails with a short reason (a sentence or two). The full reason shows in the red error bubble, with no "Show more" button.
• Trigger a run that fails with a long stacktrace. It clamps to three lines with "Show more"; clicking expands into a scrollable block, and "Show less" collapses it.
• Regression: a short reason that spans a few lines keeps its line breaks and is not cut off.

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Project	Deployment	Actions	Updated (UTC)
agenta-documentation	Ready	Preview, Comment	Jul 21, 2026 10:38am

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📝 Walkthrough

Walkthrough

Failed-run error rendering now uses a shared size heuristic to clamp large errors and conditionally show expansion controls. Expanded errors render in a scrollable preformatted block, and the related inline comment was updated.

Changes

Error rendering

Layer / File(s)	Summary
Big error display behavior web/oss/src/components/AgentChatSlice/components/AgentMessage.tsx	isBigError determines clamping and whether the Show more / Show less control appears; expanded errors render fully in a scrollable <pre>, with updated behavior documentation.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Agenta-AI/agenta#5194: Updates the Copy action to include run error text in the same error-rendering flow.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main change: showing short agent-run errors in full instead of clamping them.
Description check	✅ Passed	The description is directly related to the changeset and explains the error-display refactor in detail.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/truncate-error-message-issue

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🧹 Nitpick comments (1)

web/oss/src/components/AgentChatSlice/components/AgentMessage.tsx (1)

181-185: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Shorten comments to a single line.

As per coding guidelines, in-code comments must be kept to at most one short line unless describing genuinely surprising constraints.

• web/oss/src/components/AgentChatSlice/components/AgentMessage.tsx#L181-L185: condense the JSDoc component description into a single line (e.g., /** Failed-run body: everyday reasons show in full; big ones collapse behind a "Show more" block. */).
• web/oss/src/components/AgentChatSlice/components/AgentMessage.tsx#L532-L533: combine the inline explanation into a single line (e.g., // Failed run: the bubble reads as an inline error; everyday reasons show in full, big ones collapse.).

Source: Coding guidelines

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 3588f13 and cb2c085.

📒 Files selected for processing (1)

• web/oss/src/components/AgentChatSlice/components/AgentMessage.tsx

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Updated at 2026-07-21T10:47:03.826Z