proto: add ResolveTXT RPC

[edwardrf]

Description

Adds the ResolveTXT RPC to FabricController, mirroring the existing
ResolveIPAddr / ResolveCNAME / ResolveNS shape:

• request: domain (required) + ns_server (optional; empty = recursive from root)
• response: repeated string txts
• idempotency_level = NO_SIDE_EFFECTS

This unblocks two follow-ups:

1. Server-side handler in defang-mvp — same place that handles the existing three Resolve* RPCs (added in defang-mvp#2914). Will land separately once defang-mvp picks up the regenerated bindings via its dependency on this repo.
2. CLI client wiring in Use fabric dns client for dns resolves #2069 — that PR introduces FabricResolverClient and FabricResolver; once this proto change is merged, Use fabric dns client for dns resolves #2069 picks up ResolveTXT and adds:
   • FabricClient.ResolveTXT (interface)
   • GrpcClient.ResolveTXT (impl)
   • MockFabricClient.ResolveTXT (test stub)
   • FabricResolverClient.ResolveTXT (subset interface)
   • FabricResolver.LookupTXT (impl)

The pkg/dns.Resolver interface already gained LookupTXT (used by Azure cert validation in pkg/cli/client/byoc/azure/cert.go); the fabric resolver impl is the only Resolver still missing it once #2069 lands.

Linked issues

Prereq for #2069 and the eventual server-side change in defang-mvp.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added DNS TXT record resolution capability to the Fabric Controller service, enabling queries for domain TXT records with optional nameserver specification.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 864478f3-90cc-4e6a-958a-a97478cb2cc2

📥 Commits

Reviewing files that changed from the base of the PR and between 7902437 and e27db08.

⛔ Files ignored due to path filters (1)

• src/protos/io/defang/v1/fabric.pb.go is excluded by !**/*.pb.go

📒 Files selected for processing (2)

• src/protos/io/defang/v1/defangv1connect/fabric.connect.go
• src/protos/io/defang/v1/fabric.proto

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📝 Walkthrough

Walkthrough

A new DNS TXT record resolution RPC is added to the FabricController service. The protobuf definition introduces ResolveTXT, ResolveTXTRequest, and ResolveTXTResponse messages. The Connect-Go generated code adds corresponding client and handler interfaces, procedure constants, and complete server/client wiring for the new RPC.

Changes

ResolveTXT RPC Addition

Layer / File(s)	Summary
Protocol Contract src/protos/io/defang/v1/fabric.proto	FabricController service gains ResolveTXT RPC returning ResolveTXTResponse from ResolveTXTRequest with NO_SIDE_EFFECTS idempotency. ResolveTXTRequest carries domain and optional ns_server. ResolveTXTResponse carries repeated txts.
Client Interface & Constants src/protos/io/defang/v1/defangv1connect/fabric.connect.go	FabricControllerResolveTXTProcedure constant and ResolveTXT method signature added to FabricControllerClient interface.
Client Implementation src/protos/io/defang/v1/defangv1connect/fabric.connect.go	fabricControllerClient struct wires a new resolveTXT Connect unary client instance with schema and idempotency binding, and implements the ResolveTXT method delegating to CallUnary.
Handler Interface & Server Wiring src/protos/io/defang/v1/defangv1connect/fabric.connect.go	FabricControllerHandler interface gains ResolveTXT method. NewFabricControllerHandler creates and registers fabricControllerResolveTXTHandler binding to svc.ResolveTXT. HTTP route dispatch switch handles FabricControllerResolveTXTProcedure case.
Unimplemented Scaffold src/protos/io/defang/v1/defangv1connect/fabric.connect.go	UnimplementedFabricControllerHandler.ResolveTXT returns connect.CodeUnimplemented.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• DefangLabs/defang#2057: Adds ResolveIPAddr, ResolveCNAME, and ResolveNS RPCs to FabricController with analogous Connect-Go wiring patterns.

Suggested reviewers

• lionello
• jordanstephens

Poem

🐰 A TXT record now resolved with DNS delight,
Connect wires gleam, both client and tight,
Handler and scaffold, all perfectly placed,
The FabricController knows its new space!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'proto: add ResolveTXT RPC' directly and clearly summarizes the main change: adding a new ResolveTXT RPC endpoint to the proto definition, which is confirmed by both file summaries.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch edw/proto-resolve-txt

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.1)

level=warning msg="The linter 'gomodguard' is deprecated (since v2.12.0) due to: new major version. Replaced by gomodguard_v2."
level=warning msg="Suggested new configuration:\nlinters:\n enable:\n - gomodguard_v2\n"
level=warning msg="[linters_context] running gomodguard failed: unable to read module file go.mod: current working directory must have a go.mod file: if you are not using go modules it is suggested to disable this linter"
level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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