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Update Mode

Use this mode to evolve an existing diagram incrementally — adding new containers, removing deprecated services, or changing relationship protocols.

When it activates​

  • You paste an existing diagram and say "add X", "remove Y", "change Z"
  • "Our system now has a Redis cache — update the diagram"
  • "We migrated from MySQL to PostgreSQL — reflect that"

Example prompts​

Adding a service:

Act as the C4 Designer. Here is our current Container diagram.
We've added a Redis cache between the API and the database.
Please update the diagram.

[paste diagram]

Removing a component:

Act as the C4 Designer. Here is our current diagram.
We've decommissioned the legacy PHP frontend — remove it and update
any relationships that pointed to it.

[paste diagram]

Protocol change:

Act as the C4 Designer. We've migrated from REST to gRPC between
the API Gateway and the Orders service. Update the relationship label
and protocol tag.

[paste diagram]

Regression awareness​

The agent will flag potential regressions when you make a change:

⚠️ Removing the PHP Frontend also removes the relationship:
  Rel(legacy_php, db, "Reads user sessions from", "MySQL")

If the new React SPA also reads user sessions from the database,
you should add an equivalent Rel for it. Shall I add that?

Suggested ADR trigger​

After a significant structural change, the agent will prompt:

✅ Diagram updated. This change appears to be a significant architectural
decision (migrating from REST to gRPC). Consider documenting this using:

"Act as the adr-scribe. We just decided to use gRPC instead of REST
between the API Gateway and Orders service."