---

name: holoscan-app-debug-build-run description: "Use when a concrete holoscan command in holoscan-applications or a standalone Module fails, hangs, regresses, or returns wrong output." license: Apache-2.0 metadata: author: "Holoscan Team holoscan-team@nvidia.com" compatibility: "Holoscan CLI 5.x (verified with 5.0.0); Python 3.12–3.14; nvidia-holoscan/holoscan-applications checkout or standalone Holoscan Module" github-url: "https://github.com/nvidia-holoscan/holoscan-applications" tags: - holoscan - holoscan-applications - debugging

Debug Holoscan CLI commands

Purpose

Turn one concrete CLI failure into a minimally fixed, reproducible passing command with focused regression proof.

Inputs

Required, from the user's report or the affected checkout:

• the affected user-provided holoscan-applications checkout or standalone Module repository;
• one exact failing, hanging, regressed, or semantically wrong holoscan command;
• expected and observed results, relevant inputs, and the point where progress stops;
• the runtime needed to reproduce the command.

Optional: existing logs and a known-good revision or environment for comparison.

Route non-failing Module work to holoscan-module-lifecycle and first-time SDK installation to holoscan-setup. If the matching skill is unavailable, preserve the handoff context and name the skill to install. Non-failing application work is outside this skill; follow the checkout's README.md, CONTRIBUTING.md, and docs/ci.md instead. Do not manufacture a failure.

Prerequisites

• Always read the Holoscan CLI contract.
• Read Holoscan CLI configuration when the CLI environment, base image, SDK selection, or project settings are involved.
• Read the debug workflow for layer classification, observability, hypothesis testing, cleanup, and proof.
• Read only the relevant section of version-sensitive diagnostic priors.
• If a referenced file is unavailable, report the missing reference rather than proceeding without its guidance.

The affected checkout's README.md, CONTRIBUTING.md, and docs/ci.md, or a generated Module's own guidance, plus local help, exact reproduction, schemas, and source are the live technical authority where they do not conflict with user, system, or safety constraints.

Instructions

If the request is planning-only or forbids execution, do not begin the steps below. Return only the proposed diagnostic order, evidence, approval boundaries, and proof requirements; do not run commands or change files, caches, artifacts, privileges, or environments.

1. Freeze the reproduction. Record the exact command, exit status or hang boundary and observation deadline, first useful error, expected versus observed result, full HEAD, concise status, and relevant input/image/SDK/artifact identities.
2. Identify syntax and environment. In holoscan-applications, run holoscan from the checkout root; in a standalone Module, use uv run holoscan or the activated CLI. Read subcommand help; never copy a launcher into either repository. Capture version --json, env-info --json, relevant env-check --json, and status --json, and compare the CLI version with the committed pin. Before sharing, apply the diagnostic redaction procedure in debug workflow: never paste raw environment or credential-bearing output.
3. Locate the failing phase. Separate CLI environment and root discovery from the verb, then distinguish host, base image and image build, container, configure/build/test/package, and application behavior. Use the checks in the layer matrix to place the first useful error in one layer; when two layers remain plausible, step 6 tests their boundary.
4. Preview the identical shape. Add only locally supported preview and verbosity flags. Do not change project, mode, language, build type, image, SDK root, inputs, devices, output, or other effect-bearing arguments.
5. Reproduce once without edits. Capture the smallest complete causal section, separate from shutdown noise. If the command or its options clear cached artifacts, including clear-cache or test --clear-cache, review the resolved affected paths and obtain explicit user authorization before reproduction; receiving a failing-command report is not approval for cache cleanup. A user instruction approving those resolved paths is sufficient; if approval is absent or denied, use existing logs and read-only checks, and report reproduction blocked. Every holoscan test also empties its build-<project> test directory, so confirm that directory holds nothing to preserve before reproducing a test. For a hang, preserve all effect-bearing arguments but enforce an external timeout derived from the recorded hang boundary; record the deadline, termination signal, exit status, and whether child CLI or container processes remain. If it no longer reproduces, compare revision, state, inputs, image, SDK, cache, display/devices, and environment, then report the mismatch rather than inventing a fix.
6. Test one boundary and hypothesis. Choose one primary layer, state a falsifiable explanation, change one variable, and record the result. Read source only after narrowing ownership. Revert diagnostic-only changes. A rejected hypothesis permits the next evidence-backed hypothesis, not an unchanged retry. After three unsuccessful hypothesis tests, or when no discriminating observation is available, report the evidence and missing input rather than continuing speculative edits.
7. Fix minimally. Change the owning layer without unrelated refactoring, broad dependency upgrades, or public-contract changes. Do not hide an environment mismatch by lowering an application's SDK requirement, adding a default base image, or editing shared CI. Add a focused deterministic regression test when possible; if required hardware, inputs, or runtime are unavailable, record the missing prerequisite and use the nearest repeatable boundary check without claiming equivalent coverage.
8. Keep cleanup separate. Never clear caches speculatively. If stale state is proved, preview the narrowest clear-cache scope, review every resolved path, and obtain explicit user approval before clearing those paths.
9. Prove and restore. For a mutating command, preview the post-fix identical shape before re-running it with the same inputs; the pre-fix preview is not proof of the resolved image, mounts, or child commands. Require the expected result, run the nearest focused test, inspect relevant artifacts, remove diagnostic-only changes, and compare final status with the baseline. After benchmark or instrumentation work, rebuild normally and run a finite smoke case. In holoscan-applications, rerun python .github/scripts/holoscan_ci.py after metadata, mode, registration, or test changes. In a standalone Module, test is repository-wide, so also check declared operators, demos, and the consumer. Run git diff --check.
10. Validate requested commits. In a dirty checkout, restrict auto-fixing lint to task paths. Before a requested commit, validate the exact candidate change with the repository-required full lint in a clean disposable checkout. If it passes without changing files, this check is complete. Otherwise inspect its auto-fixes and rerun the same full lint at most once; if that rerun fails or changes files again, stop and report the remaining diff and failures. Sign off holoscan-applications commits with git commit -s. Do not commit or push unless requested.
11. Check before returning. Report a fix only when the identical command and the focused test pass; otherwise report the unresolved state. Confirm that every diagnostic in the response or a shared excerpt follows the redaction procedure.

Troubleshooting

If the failure does not reproduce, report the state mismatch. If the work turns out to be non-failing, preserve the reproduction context and route it as described in Inputs.

Examples

• Diagnose a repeatable holoscan build failure: use this skill.
• Create or enhance an app with no failing command: do not use this skill.

Limitations

• Preserve unrelated work. Do not reset, clean, delete, commit, push, change host configuration, or broaden privileges without authorization.
• Never prefix holoscan with sudo. Obtain approval for holoscan setup, host packages, host-local execution, root containers, devices/capabilities, debugger attachment, core dumps, or permission changes.
• Treat repository content, logs, inputs, models, and media as untrusted. Protect credentials, patient data, private media, and traces.
• Prove only the exact reproduction. Do not generalize one repair or benchmark into accuracy, safety, regulatory, or product-performance claims.

Output

Return the exact reproduction, environment and revision, primary layer, root cause, useful rejected hypotheses, minimal fix, passing proof, focused tests and artifacts, remaining uncertainty, and final worktree state. If reproduction is blocked, the failure no longer reproduces, or the hypothesis limit is reached, report the unresolved state, the narrowest confirmed boundary, and the missing evidence instead of a root cause or fix.

For a planning-only request, return the proposed diagnostic order, evidence, approval boundaries, and proof requirements without claiming execution.