KTOR-9293 Add empty summary default for operations

[bjhham]

Subsystem
Server, Swagger

Motivation
KTOR-9293 OpenAPI describe needs defaults

The Swagger front-end breaks when Operation is an empty object.

Solution
Added an empty string summary for the Operation type.

[coderabbitai]

Walkthrough

Changes to how empty and null summaries are handled in OpenAPI operations. Operation.Builder.summary default changed from null to empty string, merging logic updated to prefer non-empty summaries, and test assertion added to verify empty string output.

Changes

Cohort / File(s)	Summary
Operation Summary Default & Merging Logic ktor-shared/ktor-openapi-schema/common/src/io/ktor/openapi/Operation.kt, ktor-server/ktor-server-plugins/ktor-server-routing-openapi/common/src/io/ktor/server/routing/openapi/OpenApiRoutes.kt	Modified Operation.Builder.summary default initialization from null to empty string (""). Updated Operation.plus merging logic to only propagate non-empty summaries, falling back to other.summary if primary is empty, resulting in empty string if both are empty/null.
Test Assertion ktor-server/ktor-server-plugins/ktor-server-routing-openapi/jvm/test/io/ktor/server/routing/openapi/DescribeRouteTest.kt	Added assertion in annotateAddition test to verify generated OpenAPI JSON contains "summary" field with empty string value for /messages route.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: adding an empty summary default for operations, which aligns with the primary purpose of the PR.
Description check	✅ Passed	The description follows the required template with all sections completed: Subsystem (Server, Swagger), Motivation (references KTOR-9293 and explains the Swagger front-end issue), and Solution (describes adding empty string summary).

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✨ Finishing touches

• 📝 Generate docstrings

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[zibet27]

Can we make it non-nullable?

[bjhham]

That would be a breaking change 😞

[zibet27]

Looks like io.ktor.openapi.OperationSerializationTests.operation with tags and external docs()[jvm] is failing

[bjhham]

Yeah it seems that the empty string uncovered a bug in the YAML parser.

It creates something like:

summary:
responses:
  200: yadda yadda

Then interpreting responses as being part of summary. YAML is hard.