test(agent-runtime): harden slash command regressions (#543)

[yacosta738]

Related Issues

Fixes #543
Related to #527

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Summary

This PR hardens slash-command regression coverage for the existing registry-backed session commands.

It adds focused transport-edge regressions for the highest-value remaining gaps only: CLI denied /resume {session_id}, gateway SSE denied /resume {session_id}, gateway SSE invalid /tldr extra args, and recognized slash handling on a gateway-facing plan-mode path. The goal is to freeze current behavior and prevent drift while the slash-command platform continues to evolve.

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Tested Information

Validated with focused and full Rust runtime checks:

• cargo test --manifest-path clients/agent-runtime/Cargo.toml cli_resume_target_without_caller_scope_preserves_denied_error_path -- --nocapture
• cargo test --manifest-path clients/agent-runtime/Cargo.toml gateway::tests::web_chat_stream_ -- --nocapture
• cargo fmt --manifest-path clients/agent-runtime/Cargo.toml --all -- --check
• cargo clippy --manifest-path clients/agent-runtime/Cargo.toml --all-targets -- -D warnings
• cargo test --manifest-path clients/agent-runtime/Cargo.toml
• pre-push hook: Rust checks + runtime suite (3565 tests passed)

Reviewers should focus on:

• the new CLI denial regression in clients/agent-runtime/src/main.rs
• the new SSE regressions in clients/agent-runtime/src/gateway/mod.rs
• the spec sync for targeted regression-hardening scope in openspec/specs/slash-command-registry/spec.md

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Documentation Impact

• Docs updated in:
  • openspec/specs/slash-command-registry/spec.md
  • openspec/changes/archive/2026-04-18-slash-command-regression-tests/
• No docs update required because:
• I verified the documentation matches the current behavior.

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Breaking Changes

None.

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Checklist

• I have checked that there isn’t already a PR solving the same problem.
• I have read the Contributing Guidelines.
• I ensured my code follows the project's style guidelines.
• I have added or updated tests that prove my fix is effective or that my feature works.
• I have updated the documentation, or I explained above why no documentation update is needed.
• I verified the documentation matches the current behavior.
• I have documented any breaking changes in the Breaking Changes section.
• I have linked the related issue (if any).

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📥 Commits

Reviewing files that changed from the base of the PR and between 91d9a05 and 31d459b.

📒 Files selected for processing (10)

• clients/agent-runtime/src/gateway/mod.rs
• clients/agent-runtime/src/main.rs
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/design.md
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/exploration.md
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/proposal.md
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/specs/slash-command-registry/spec.md
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/state.yaml
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/tasks.md
• openspec/changes/archive/2026-04-18-slash-command-regression-tests/verify-report.md
• openspec/specs/slash-command-registry/spec.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/dallay-543-slash-regression-tests

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[github-actions]

✅ Contributor Report

User: @yacosta738
Status: Passed (12/13 metrics passed)

Metric	Description	Value	Threshold	Status
PR Merge Rate	PRs merged vs closed	90%	>= 30%	✅
Repo Quality	Repos with ≥100 stars	0	>= 0	✅
Positive Reactions	Positive reactions received	11	>= 1	✅
Negative Reactions	Negative reactions received	0	<= 5	✅
Account Age	GitHub account age	3094 days	>= 30 days	✅
Activity Consistency	Regular activity over time	108%	>= 0%	✅
Issue Engagement	Issues with community engagement	0	>= 0	✅
Code Reviews	Code reviews given to others	571	>= 0	✅
Merger Diversity	Unique maintainers who merged PRs	2	>= 0	✅
Repo History Merge Rate	Merge rate in this repo	92%	>= 0%	✅
Repo History Min PRs	Previous PRs in this repo	249	>= 0	✅
Profile Completeness	Profile richness (bio, followers)	90	>= 0	✅
Suspicious Patterns	Spam-like activity detection	1	N/A	❌

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_{Contributor Report evaluates based on public GitHub activity. Analysis period: 2025-04-18 to 2026-04-18}