feat(agents): reuse existing agent.yaml on init from existing code

[hund030]

Closes #7268.

Summary

When azd ai agent init runs in a directory that already contains a bare agent.yaml definition (no template: wrapper), reuse it instead of either prompting to overwrite (interactive) or failing with CodeInvalidAgentManifest: agent.yaml already exists at ... (--no-prompt, added in #8266). Matches the issue's wording: "if it's a definition, then we have less to ask and just setup azure.yaml."

The manifest half of the issue is already handled by upstream detectLocalManifest and is unchanged.

Changes

• cmd/init.go RunE: new detection block alongside detectLocalManifest. A user with a local agent.yaml skips both the init-mode prompt and the from-code scaffolding. Symmetric confirmation prompt (auto-yes under --no-prompt). Tracks manifestDetectedButDeclined so a declined manifest is not re-discovered and mis-classified.
• cmd/init_from_code.go: retained the agent.yaml already exists guard from add 'azd ai agent sample list' to browse templates and improve non-interactive init #8266 (using findExistingAgentYaml so it covers all four candidate filenames). The guard now only fires on the decline-reuse fallback path (user declines the RunE prompt and then picks "Use the code in the current directory"); it prevents silent overwrite. Lang detection in addToProject is limited to bare-definition filenames so a leftover manifest cannot short-circuit detection.
• cmd/init_from_code_reuse.go (new): findExistingAgentYaml, runReuseDefinition, loadAgentDefinitionFile. Runs full agent_yaml.ValidateAgentDefinition (catches missing/invalid kind, name format, kind-specific structural checks), bootstraps project + env, normalizes absolute --src to project-relative, calls existing addToProject. Error/info messages use the actual detected filename so users with agent.yml see agent.yml, not a hardcoded agent.yaml. The on-disk file is never rewritten.
• Foundry project resolution is intentionally skipped on this path (out of scope per the issue's "less to ask" wording). Users needing it can set AZURE_AI_PROJECT_ID or use the manifest pipeline.

Unit tests in cmd/init_from_code_reuse_test.go cover findExistingAgentYaml (filename precedence, shallow scan), loadAgentDefinitionFile (happy path + reject manifest-shaped, missing kind, invalid name, broken yaml), and the runReuseDefinition failure branches that short-circuit before any azd gRPC calls.

Verification

Manual e2e on Windows against the locally-built CLI:

Scenario	Before	After
bare agent.yaml + --no-prompt	agent.yaml already exists at ... exit 1	reuse, exit 0
bare agent.yaml interactive, accept reuse prompt	mode prompt -> overwrite prompt -> proceed	single "Use it?" prompt -> reuse
bare agent.yaml interactive, decline reuse prompt -> pick "from code" mode	scaffold silently overwrites the file	overwrite guard fires; default-no protects the file
agent.manifest.yaml	upstream ok	upstream ok (unchanged)
broken agent.yaml	overwrite-related error	structured CodeInvalidAgentManifest referencing the actual filename
no agent.yaml	scaffold flow	unchanged

Related

• Design spec PR: doc: design spec for azd ai agent init reuse of existing agent.yaml #8325
• Issue: Allow azd ai agent init to detect and reuse an existing agent.yaml #7268
• Follow-up: Foundry project resolution for the definition path (out of scope here)

[github-actions]

📋 Prioritization Note

Thanks for the contribution! The linked issue isn't in the current milestone yet.
Review may take a bit longer — reach out to @rajeshkamal5050 or @kristenwomack if you'd like to discuss prioritization.

[Copilot]

Pull request overview

This PR updates the azd ai agent init flow in the Azure AI Agents extension to detect an existing bare agent.yaml (definition-only, no template: wrapper) and reuse it instead of overwriting/failing, aligning with #7268.

Changes:

• Add a pre-dispatch detection step in init to find and optionally reuse an existing bare agent definition YAML.
• Remove the earlier agent.yaml already exists guard from the from-code init path (intended to be handled by the new upstream dispatch).
• Add a new reuse implementation that loads an existing definition and wires it into azure.yaml without rewriting the definition file.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
cli/azd/extensions/azure.ai.agents/internal/cmd/init.go	Adds detection/prompting to reuse an existing bare agent definition before prompting for init mode / scaffolding.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_from_code.go	Removes the pre-flight overwrite protection for existing agent.yaml in the from-code path.
cli/azd/extensions/azure.ai.agents/internal/cmd/init_from_code_reuse.go	New helpers to locate, parse, and reuse an existing definition file and update azure.yaml.

Comments suppressed due to low confidence (1)

cli/azd/extensions/azure.ai.agents/internal/cmd/init_from_code.go:87

• The overwrite guard for an existing agent.yaml was removed, but writeDefinitionToSrcDir still unconditionally writes srcDir/agent.yaml. If the user declines the new “reuse existing definition” prompt upstream, the from-code path will now silently overwrite the existing file (data loss). Reintroduce an overwrite confirmation here (or ensure init.go treats “decline reuse” as a cancellation / requires --force before overwriting).

	// No manifest pointer provided - process local agent code
	// Create a definition based on user prompts
	localDefinition, err := a.createDefinitionFromLocalAgent(ctx)
	if err != nil {
		return fmt.Errorf("failed to create definition from local agent: %w", err)

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.