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What we found by running it.

Four notes from building a memory layer. Mostly the decisions that were hard to reverse, and one bug that a green test suite was never going to catch.

Stacked sheets of glass, each slightly out of alignment with the one below
Operations7 min read

Seven migrations, proved correct, never applied

CI ran them against a throwaway container on every commit. Nothing ever compared them against the database anyone was using, and the dashboard that would have shown the damage was inside it.

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A doorway framed in a wall that leads to open sky
Auth5 min read

Every OAuth flow ended on a 404, at the last step

The API had been redirecting people to a consent screen that did not exist. Everything before it worked, which is why nobody noticed.

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A staircase ending flush against a blank wall
Testing6 min read

The code was written. Nothing called it.

Threading headers parsed correctly by a helper the parser never invoked. Four tests written afterwards found it in seconds, which is the argument for the tests.

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Rows of identical bottles with a few filled darker than the rest
Observability6 min read

The dashboard said failures are kept in full. It was wrong.

Building observability that costs nothing per request means sampling. Getting the sampling right is easy; describing it honestly on the screen turned out to be the harder half.

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A single brass key on an empty table
Auth4 min read

A short password answered 500

A deliberate, well-worded policy rejection reached the client as an internal server error, because the error class was missing one field.

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Long grass cut into narrow bands of light
Ingestion6 min read

Eighty characters of signal, and no memories at all

A bounded regex meant the extractor could read a short sentence and nothing longer. 521 ingestion tests passed against a detector that produced nothing from an ordinary paragraph.

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A row of old brass keys hanging on hooks
Auth5 min read

Re-authorising an account revokes the connection before it

Disconnecting inside ChatGPT tells us nothing. The only signal we ever get that a connection is over is the person making a new one, so making a new one has to end the old one.

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An industrial electrical panel with rows of switches
Reliability7 min read

Circuit breakers that hold work instead of dropping it

When the model that reads a scanned page is down, refusing the upload solves our problem by losing the user's. The bytes go to storage, the job waits in Postgres, and the person gets told.

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Deep shelves of bound archive volumes receding into shadow
Memory model7 min read

Superseded, not overwritten, so March is still there

When a memory changes, the old one gains an end date and a pointer forward. Both survive, which is what lets one store answer both what is true now and what was true then.

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