docs: state the mocking convention

[retr0h]

States the mocking convention in this repository, as repo-standards requires: a repository states in full the conventions it is held to, and the rule was in the corpus and in no repository.

Implements rescope-go-code-standards task 5.4. The rule itself landed in osapi-io/specs#96.

What the section says

• A double for an interface this organization defines is generated with mockgen and committed. Do not hand-write a struct to satisfy one.
• Generated mocks live in a mocks package beside the code they mock, produced by a generate.go holding the //go:generate directive.
• The generator resolves through the module's tool dependencies, so every checkout runs the version go.mod records.
• gen/ is reserved for API code generation — mocks do not go there.
• Where call sites repeat the same expectations, write a constructor returning a configured mock rather than introducing a hand-written type.

Three doubles stay hand-written, because generating them buys nothing: stdlib interfaces, doubles carrying a real implementation, and recorders for a dependency called from a goroutine the test cannot join.

Identical in all five

The shared Code standards block hashes the same in gohai, nats-client, nats-server, osapi-orchestrator, and osapi — so a difference in wording would mean a difference in rule.

Docs only. just md-fmt-check passes.

Next: the implementations get fixed — gohai's four Collector doubles and internal/executor/gen/, and osapi-orchestrator's mockRenderer.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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##             main     #453   +/-   ##
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  Coverage   99.94%   99.94%           
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  Files         484      484           
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  Misses         14       14           

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