[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

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This section details on the original issue you should resolve

<issue_title>[deep-report] Actionable repo-slug validation errors (repoutil + 3 pkg/cli call sites)</issue_title>
<issue_description>### Description

pkg/repoutil/repoutil.go:20's SplitRepoSlug returns fmt.Errorf("invalid repo format: %s", slug) with no expected format or example, contradicting the repo's own .github/skills/error-messages/SKILL.md style guide. The same bare pattern is duplicated in pkg/cli/preconditions.go:170, pkg/cli/fetch.go:95, and pkg/cli/outcome_eval.go:518 (each phrased slightly differently: "invalid repository format", "invalid repository slug", "invalid repo for root tracing"). Verified live at all 4 locations on main (commit f2e8122).

Fix

Update all 4 call sites to the skill's template — what's wrong, what's expected, an example — using consistent wording, e.g.:

fmt.Errorf("invalid repo format %q — expected 'owner/repo' format (for example: 'github/gh-aw')", slug)

Update/add tests asserting the new message text. Run make fmt. No behavior change, string-only.

Expected Impact

Users/agents hitting a malformed repo slug get an actionable fix path instead of a bare echo of their input, reducing debugging round-trips.

Suggested Agent

Copilot coding agent (mechanical string change + test update).

Estimated Effort

Quick (< 1 hour)

Data Source

DeepReport Intelligence Briefing 2026-08-21, mining discussion #54543 (Repository Quality Improvement Report - Error Message Actionability), Tasks 1-2.

Generated by 🔬 Deep Report · agent · 106.7 AIC · ⌖ 8.62 AIC · ⊞ 12.4K · ◷

• expires on Aug 23, 2026, 10:30 AM UTC-08:00

• Closes [deep-report] Actionable repo-slug validation errors (repoutil + 3 pkg/cli call sites) #54580

Comments on the Issue (you are @copilot in this section)

• Fixes [deep-report] Actionable repo-slug validation errors (repoutil + 3 pkg/cli call sites) #54580