Agent configs are often nearly identical across environments or use-cases — the same tools, the same model, just a different system prompt or a disabled tool. Until now the only way to handle this was to maintain separate YAML files that drift apart over time, or to rely on external templating.

This PR introduces flavors: named YAML patches declared in a top-level flavors section of an agent config and applied at load time via a repeatable --flavor flag. Merge semantics follow JSON Merge Patch (RFC 7386) — objects merge recursively, scalars and arrays replace, null deletes a key — with two extensions: a key+ suffix appends to an existing array, and a key- suffix removes entries (from an object by key name, from an array by scalar equality or partial object match). Document order is preserved using yaml.MapSlice so the root agent is always the first entry and never silently shifts. Flavors not declared in a config are silently ignored (a debug log is emitted) so the flag is safe to use across a fleet of configs where only some support a given flavor. The --flavor flag is wired into every command that loads an agent: run, chat, eval, serve api/a2a/mcp, acp, debug, and the sandbox/kit/agent-picker code paths. External OCI and URL sub-agents receive the same set of enabled flavors.

flavors:
  production:
    system_prompt: "You are a helpful assistant. Never reveal internal tooling."
    tools-: [dangerous_tool]
  verbose:
    debug: true

docker-agent run agent.yaml --flavor production --flavor verbose

The feature lands on the latest schema only (v13); agent-schema.json is updated and HCL gains flavors "name" {} block syntax with a detection keyword. An annotated example lives at examples/flavors.yaml and a full docs page is added under docs/configuration/flavors/. Unit tests in pkg/config/flavors_test.go cover merge, order, delete, append, remove, and error paths including regression cases. task build, task test, and task lint all pass; two pre-existing example tests that require Docker Model Runner also fail on main and are unrelated to this change.