David debugged: Investigated why lecture notes generation was failing and took 20+ minutes

After seeing multiple failure toasts, stale 'Preparing' states, and success toasts from old candidates appearing on new clicks, David opened a wide-ranging investigation:

why is the lecture notes generation failing in the first place? go to production logs and figure it out. why is there more than 1 toast failure showing? does your fix actually fix this or just reduce the length of time for stale toasts? why dont they say retry on the pill instead of preparing?

When timing data showed a generation had taken 21 minutes, David immediately asked why:

why did it take over 20 minutes to complete? go investigate each sequential sub agent that ran, whether there were TPM limits causing it to wait, or what else caused the length

The investigation revealed a sequential 3-step pipeline with describer agents between each step. David then asked whether the steps truly depended on each other's output — wanting to know if parallelization was safe — and probed the question carefully:

okay but youre not making sense. you said that the lecture note sequential agent at step k doesnt depend on any input from the sequential agent at step k-1. but if its being fed the output from step k-1's describer agent, then it does depend on it. go and actually study whether the output from the describer agent at step k-1 is being fed to the lecture notes sequential agent at step k