feat: sticky-comment-and-job-summary

[CodeYogiCo]

Two reporting features that build on the existing reporter seam and share the report Markdown.

Sticky PR comment

Previously the plugin POSTed a new comment on every push, stacking duplicates on active PRs. Now github_pr.go first GETs the PR's comments and, if it finds the one carrying a hidden marker (<!-- pull-request-code-coverage:patch-coverage -->), PATCHes that comment in place; otherwise it POSTs a new one. A single, always-current coverage comment.

Job summary ($GITHUB_STEP_SUMMARY)

New StepSummary reporter writes the same Markdown to $GITHUB_STEP_SUMMARY when set, so coverage renders on the Actions run page — visible even on fork PRs where the read-only token can't post a comment (pairs with the earlier fork-PR change). The workflow now mounts and passes the summary file.

Refactor

Extracted the shared buildMarkdownReport used by both the PR comment and the job summary, and added Unmarshal to the JSON client (to read the comments list).

Tests / docs

• New step_summary_test.go; reworked github_pr_test.go for the GET→PATCH/POST flow (incl. a sticky-update case); mock GitHub API and golden bodies updated for the new GET call and marker.
• go test ./..., gofmt, and golangci-lint run all clean.
• README + AGENTS.md updated.

🤖 Generated with Claude Code

[github-actions]

🛡️ Patch Coverage Report

Scope: changed lines only — the code this PR adds or edits, not whole files or the repo. It answers one thing — did your tests run the code you just touched?

Diff coverage: 81% 🟢 — 88 of 108 changed instructions covered

Metric	Value
🟢 Covered instructions	88 (81%)	changed code your tests executed
🔴 Missed instructions	20 (19%)	changed code your tests never ran
📈 Tracked changed lines	108 (34%)	lines the coverage tool could measure
⚪ Untracked changed lines	213 (66%)	comments, blanks, declarations

_{Lines = the source lines you changed. Instructions = the executable units the coverage tool counts inside those lines — one line can hold several (e.g. JaCoCo bytecode), so the two counts differ.}

Coverage by file

File	Diff coverage	Covered / Missed
internal/plugin/pluginjson/mocks.go	🔴 0%	0 / 5
internal/plugin/runner.go	🔴 10%	1 / 9
internal/plugin/reporter/step_summary.go	🟢 88%	14 / 2
internal/plugin/reporter/github_pr.go	🟢 94%	62 / 4
internal/plugin/pluginjson/client.go	🟢 100%	3 / 0
internal/test/mocks/mock_gh_api.go	🟢 100%	8 / 0

_{7 changed file(s) with no measurable lines (config, docs, generated, or test-only) omitted.}

🔍 Uncovered lines (20)

--- internal/plugin/pluginjson/mocks.go:23
func (m *MockClient) Unmarshal(data []byte, v interface{}) error {
--- internal/plugin/pluginjson/mocks.go:24
	args := m.Called(data, v)
--- internal/plugin/pluginjson/mocks.go:25

--- internal/plugin/pluginjson/mocks.go:26
	return args.Error(0)
--- internal/plugin/pluginjson/mocks.go:27
}
--- internal/plugin/reporter/github_pr.go:141
		return 0, errors.Wrap(readErr, "Failed reading github comments response")
--- internal/plugin/reporter/github_pr.go:142
	}
--- internal/plugin/reporter/github_pr.go:150
		return 0, errors.Wrap(unmarshalErr, "Failed parsing github comments response")
--- internal/plugin/reporter/github_pr.go:151
	}
--- internal/plugin/reporter/step_summary.go:30
		return errors.Wrap(err, "Failed writing job summary")
--- internal/plugin/reporter/step_summary.go:31
	}
--- internal/plugin/runner.go:162
		// nolint: gosec // path comes from the trusted GitHub Actions runner env
--- internal/plugin/runner.go:163
		summaryFile, openErr := os.OpenFile(summaryPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
--- internal/plugin/runner.go:164
		if openErr != nil {
--- internal/plugin/runner.go:165
			return errors.Wrap(openErr, "Failed opening GITHUB_STEP_SUMMARY file")
--- internal/plugin/runner.go:166
		}
--- internal/plugin/runner.go:167
		defer func() {
--- internal/plugin/runner.go:168
			_ = summaryFile.Close()
--- internal/plugin/runner.go:169
		}()
--- internal/plugin/runner.go:171
		reporters = append(reporters, reporter.NewStepSummary(summaryFile))

_{🤖 Generated by pull-request-code-coverage — coverage for changed lines only.}