My Agent Shipped a Broken Chart and Told Me It Was Done

A developer built GuardianKane, a verification layer for Claude Code that placed 2nd in the TestMuAI Kane CLI hackathon, after an AI agent marked a task complete while shipping a performance chart that rendered the same data series twice. The tool uses Claude Code's Stop hook to block an agent from finishing until TestMuAI's Kane CLI browser agent runs headless Chrome tests against the running dev server, allowing the agent to claim a task done but reserving the KANE_VERIFIED state for the hook alone. In four paired experiments, including the dense ORBITAL dashboard where the doubled chart appeared, the gated builds were compared against unassisted agents given the same PRDs.

The chart looked fine in the code. The data pipeline was correct. The chart library call had the right shape. Every prop was passed, every array was populated, and nothing about the component would have looked suspicious in thirty seconds of review. If you had put that diff in front of me cold, I would have approved it. Then I opened the page. The performance chart was rendering the same series twice: two overlapping traces at slightly different weights, a smeared, doubled line that no one would ship on purpose. The same series, drawn twice. This build reported the task complete. The agent that wrote it had already marked the task done. This series is about that word, "done", and what it took to stop trusting it. It starts with a tool I built for the TestMuAI Kane CLI hackathon, where it placed 2nd. GuardianKane did not start as a verifier. The first four commits in the repo are a planning tool: a design spec, an implementation plan, a task-tracker library, and a Claude Code skill with a thin kane-cli wrapper. You gave it a PRD and got back a task-tracker.md : tasks with ids, titles, the PRD lines each one implements, and dependencies. It was tidy, and it had one hole in the middle. The agent worked through the tracker and moved each task to done when it decided the task was done. Nothing checked. The tracker was a list of claims, and the planner's whole output depended on believing them. The same afternoon, commit 896bc57 added two Claude Code hooks, and the planner became a gate. Claude Code has a hook called Stop . It fires every time the agent finishes a turn and is about to hand control back. If the hook prints {"decision": "block"} with a reason, the agent does not stop. It reads the reason and keeps working. That is the entire lever. Everything else is what I put behind it. The agent never calls Kane itself. The hook does, every time it tries to stop. The tracker grew a state machine. The agent may move a task to IN PROGRESS and CLAIMED DONE . Only the hook is supposed to write KANE VERIFIED . The asymmetry is the point: the agent can say it is done; it cannot say it is verified. When a task is CLAIMED DONE and the agent tries to stop, the hook drives Kane CLI https://testmuai.com , TestMuAI's browser agent, against the running dev server in a real headless Chrome. Two checks run per task: kane-cli testmd run <file --agent --headless --variables <json , with start url pointed at the local server. If either fails, the hook denies the stop with a reason written for the agent: the task, the attempt count, Kane's summary of what failed, and one instruction. Flip the task back to IN PROGRESS , fix the code, and claim done again. There is no path from "the browser proved this broken" back to "done" that does not go through the code. Two hook entries in .claude/settings.json are the whole Claude Code side: { "hooks": { "Stop": { "hooks": { "type": "command", "command": ".claude/hooks/guardian-kane-stop.sh" } } , "PostToolUse": { "matcher": "Edit|Write", "hooks": { "type": "command", "command": ".claude/hooks/guardian-kane-post-tool-use.sh" } } } } PostToolUse quietly records which files each task touched. In this shape of the tool nothing reads that record. Hold on to it; it becomes the most important data in the project later. To find out whether any of this mattered, I ran four paired experiments. Each pair is the same PRD given to two builds: one unassisted Claude Code agent told "build this", and one going through the full GuardianKane loop. The PRDs were a todo app, a room booking widget, a higher-fidelity booking studio, and ORBITAL: a dense single-page institutional portfolio dashboard with twelve or so interactive subsystems. ORBITAL is where the chart came from, because it is the only one of the four with enough visual density to have somewhere to hide. The gated build, orbital-kane , rendered one clean trend line and a visually distinct dashed benchmark, which is what the PRD asked for. orbital-kane . One series, one line. The unassisted build, orbital-baseline , drew the doubled line at the top of this post. It also drifted on the alerts panel. The PRD specifies a single-column, full-width, stacked alert list where one alert expands at a time. The baseline built a compact two-column grid instead. orbital-kane . Full width, stacked, one expanded. orbital-baseline . Two columns, and the gaps do not match the panels beneath it. The same screenshot shows a third problem: the space around the alerts block does not match the space around the holdings and risk cards directly below it. Three defects in one build, and not one of them is visible in a diff. A grid class is not wrong-looking. A chart component that renders one series twice is well formed. The bugs only exist at the moment of render, so the only way to find them is for something to look at the rendered page. Going in, I assumed the scripted replay was the valuable half of the gate. It is deterministic and repeatable; it is what you would build first. I built the sweep almost as an afterthought and was mildly embarrassed by how fuzzy it was. The ORBITAL activity log says otherwise. Twelve tasks, all twelve reached KANE VERIFIED . The sweep flagged something exactly once, on T7, the alerts panel. Both scripted tests for T7 had just passed. They covered expand and switch behavior and asserted nothing about layout. The sweep failed the task anyway and sent it back to IN PROGRESS . About 43 minutes later the tests passed again and the sweep came back clean. That log line carries no summary text, so I cannot tell you what the sweep saw. The alerts panel is the same panel the unassisted build got wrong, which is a tempting story. I have no data connecting the two, so I am not telling it. What I can say is that it was the only failure in the whole build that was a real problem with the app. And the pattern underneath it is general: a scripted test can only check what you thought to assert. The defects that ship are, almost by definition, the ones nobody thought to assert. A strategy made only of assertions written in advance cannot catch the thing most likely to hurt you. Exit codes lie, in both directions. I first mapped kane-cli 's exit code straight into the gate. A replay could exit 1 while its own final run end line reported status: 'passed' with every step passing. A sweep could exit 0, because the objective "completed", while its verdict reported a confirmed bug. The hook now parses the last structured line and trusts the verdict over the process status. If you wire any agentic tool into a gate, read its structured output. The exit code is a summary of a summary. Killing the process does not kill the browser. kane-cli spawns its own runner, and under it the headless Chrome instances. A timeout that kills the child you spawned leaves those running as orphans, still holding a debugging port. The fix is to spawn detached, so the child leads its own process group, and kill the whole group after every run: function killProcessGroup pid { if pid return; try { process.kill -pid, 'SIGKILL' ; } catch { // ESRCH: group already empty } } The naive reading is "agents are unreliable, add tests." That was already the advice before I started, so it is not a finding. The more precise reading is that the failure was never in the code generation. Claude wrote a chart component that was, structurally, fine. The failure was in the self-report. An agent saying "done" is an assertion with no evidence attached, and my first tool had treated that assertion as a state transition. I have to be careful about what the gated build proves. Its chart was right, but the log does not show the gate catching a doubled chart and forcing a fix. The gated build also had its PRD grilled for ambiguity before any code existed, and twelve tasks each scoped to a PRD section. Which of those made the difference, one pair of builds cannot tell me. The narrower claim holds. In the gated build, nothing reached "done" on the agent's word. In the unassisted build, "done" was a sentence, and the sentence was wrong. There is a version of this that is just CI, and for a lot of projects CI is enough. What CI does not give you is a check inside the agent's own loop, before it stops, while it still has the context to fix what it broke. By the time CI goes red, the session is over. The gate fires while the agent is still standing there. The rest of this series is about the two surprises that followed. The first is where the gated build's advantage actually came from, and it was not the browser. The second is that of the eight ORBITAL tasks that failed a check, seven were not the app's fault at all. Part 1 of 3. Next: the requirement nobody wrote https://abhinavpangaria.pages.dev/dispatches/the-requirement-nobody-wrote , on the question that separated the builds and the experiment that found nothing. The code is at github.com/18Abhinav07/adventures-with-kane https://github.com/18Abhinav07/adventures-with-kane . Part 1 of Your Agent Might Actually Lie to You https://abhinavpangaria.pages.dev/dispatches/series/your-agent-might-lie . The original, with the full series navigation, is on my site https://abhinavpangaria.pages.dev/dispatches/agent-shipped-a-broken-chart .