fix: allow null errors in successful adapter results

[zhongxuanwang-nv]

Overview

Synchronizes the adapter-result schema with the Rust runtime behavior: a successful result can include "error": null, but never a non-null error. This fixes the TypeScript projection failure exposed by PR #188 without bringing in its unrelated changes.

• I confirm this contribution is my own work, or I have the right to submit it under this project license.
• I searched existing issues and open pull requests, and this does not duplicate existing work.

Details

• Update the canonical Rust schema and regression coverage.
• Update the guarded TypeScript projection, generated declaration, and packaged schema copy.
• Add type-level coverage for a successful result with error: null.

Validation

• cargo fmt --all -- --check
• just schemas
• just test-rust
• just test-typescript
• git diff --check

Not run: just test-python (deferred at request).

Where should the reviewer start?

Start with crates/fabric-core/src/agent_execution.rs and typescript/adapter-contract/scripts/generate.mjs; they define the canonical JSON Schema conditional and its TypeScript discriminated-union projection.

Related Issues: (use one of the action keywords Closes / Fixes / Resolves / Relates to)

• Relates to: fix: reject colliding tool definition extensions #188

Summary by CodeRabbit

• Bug Fixes

  • Successful agent results now consistently support an explicitly null error value.
  • Updated result validation and type definitions to accept successful responses with error: null.

• Documentation

  • Clarified that successful results may omit error or set it to null, while non-null errors remain invalid.

• Tests

  • Added coverage confirming successful results with null output and null error are valid.
  • Updated execution test fixtures to reflect the clarified result format.

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For learning-oriented and developer content, do not force trademark symbols unless explicitly required; for press, ...

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🧠 Learnings (2)

📚 Learning: 2026-08-07T07:15:59.993Z

Learnt from: AnuradhaKaruppiah
Repo: NVIDIA/NeMo-Fabric PR: 186
File: docs/adapter-contract/registration-and-discovery.md:103-104
Timestamp: 2026-08-07T07:15:59.993Z
Learning: Keep documentation files under docs/adapter-contract/ in portable Markdown (.md), not MDX. GitHub and the public authoring skill consume these files directly, and the NVIDIA NeMo Fabric documentation pipeline accepts them without conversion; do not flag the lack of MDX conversion for these files.

Applied to files:

• docs/adapter-contract/results.md

📚 Learning: 2026-08-07T16:20:01.603Z

Learnt from: AnuradhaKaruppiah
Repo: NVIDIA/NeMo-Fabric PR: 186
File: docs/adapter-contract/README.md:1-4
Timestamp: 2026-08-07T16:20:01.603Z
Learning: For maintained Markdown files under docs/adapter-contract/, Fern parses content as MDX. Write SPDX license headers as JSX comments (`{/* ... */}`), not HTML comments, because HTML comments cause Fern parsing failures. This JSX form is accepted by the repository copyright checker and validated by Docs Preview.

Applied to files:

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🔇 Additional comments (3)

crates/fabric-core/src/schema.rs (1)

450-453: LGTM!

docs/adapter-contract/results.md (2)

34-37: LGTM!

---

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---

Walkthrough

Successful AgentRunResult schemas now support an omitted or explicit error: null value for succeeded results. Rust and TypeScript contracts, projections, guards, tests, and documentation are aligned.

Changes

Agent result contract alignment

Layer / File(s)	Summary
Successful result schema constraints crates/fabric-core/src/agent_execution.rs, schemas/adapter-contract/agent-run-result.schema.json, typescript/adapter-contract/schemas/agent-run-result.schema.json, typescript/adapter-contract/scripts/projection-guards.mjs	Successful-result schema branches allow error only when its value is null.
Projection and validation updates typescript/adapter-contract/scripts/generate.mjs, crates/fabric-core/src/schema.rs, typescript/adapter-contract/test/execution.test.ts, docs/adapter-contract/results.md	The TypeScript projection permits an optional null error. Validation cases and documentation cover omitted and explicit null error values.

Estimated code review effort: 2 (Simple) | ~10 minutes

Mergeability Score: 🔵 Low · up to 04522

The PR updates adapter-contract documentation, but the required documentation build has not been run or recorded. This is a bounded merge-readiness gap with no indicated product or runtime impact; merge is reasonable once just docs passes.

Possibly related PRs

• NVIDIA/NeMo-Fabric#203: Introduces the related TypeScript AgentRunResult schema, projection, and guard definitions.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses valid Conventional Commits syntax, describes the schema change, stays under 72 characters, and has no trailing period.
Description check	✅ Passed	The description includes the overview, reviewer starting points, related issue, required confirmations, implementation details, and validation results.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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Inline comments:
In `@crates/fabric-core/src/schema.rs`:
- Around line 450-454: Add a second succeeded-result validation assertion
alongside the existing fixture in the validator test, omitting the error
property entirely while retaining the successful status and null output. Keep
the existing error: null case unchanged and verify both forms are accepted.

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**/*

📄 CodeRabbit inference engine (.agents/skills/karpathy-guidelines/SKILL.md)

**/*: Before implementing, explicitly state assumptions, surface ambiguity and tradeoffs, present multiple interpretations when relevant, and ask for clarification rather than silently deciding or proceeding when requirements are unclear.
Prefer the minimum code needed to solve the requested problem: avoid speculative features, unnecessary abstractions, unrequested flexibility, and handling of impossible scenarios; simplify overcomplicated solutions.
When editing existing code, make surgical changes only: do not modify unrelated code, comments, formatting, or pre-existing dead code; match the existing style, and remove only unused imports, variables, or functions introduced by your changes.
Define verifiable success criteria for each task, such as writing regression tests for bugs and invalid-input tests for validation, then verify the implementation against those criteria. For multi-step work, state a brief plan with a verification check for each step.

**/*: Always spell NVIDIA in all caps; do not use Nvidia, nvidia, nVidia, nVIDIA, or NV.
Use an NVIDIA before a noun, because the name begins with an “en” sound.
Do not add a registered trademark symbol after NVIDIA when referring to the company; use trademark symbols with product names only when required by the document type or legal guidance.
Verify official capitalization, spacing, hyphenation, and spelling for NVIDIA and third-party product names; do not rewrite official product names for grammar or title-case rules.
Precede NVIDIA product names with NVIDIA on first mention when natural and accurate, and link the first mention when the destination helps the reader.
On first use, include the company name and full model qualifier when it helps identify the model; preserve official capitalization and punctuation, and use shorter family names only after establishing the full name.
For learning-oriented and developer content, do not force trademark symbols unless explicitly required; for press, ...

Files:

• typescript/adapter-contract/scripts/projection-guards.mjs
• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs
• typescript/adapter-contract/test/execution.test.ts
• typescript/adapter-contract/scripts/generate.mjs
• typescript/adapter-contract/schemas/agent-run-result.schema.json
• schemas/adapter-contract/agent-run-result.schema.json

**/*.rs

📄 CodeRabbit inference engine (.agents/skills/contribute-api/SKILL.md)

Implement new runtime or binding behavior in the shared Rust core first.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,py,pyi,json,yaml,yml}

📄 CodeRabbit inference engine (.agents/skills/contribute-api/SKILL.md)

Determine and update every affected public surface, including the CLI, PyO3 bindings, Python SDK, type stubs, schemas, and adapter contract, so they remain in parity.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs
• typescript/adapter-contract/schemas/agent-run-result.schema.json
• schemas/adapter-contract/agent-run-result.schema.json

**/*.{rs,toml}

📄 CodeRabbit inference engine (.agents/skills/prepare-pr/SKILL.md)

For any Rust change, run just test-rust and cargo fmt --all -- --check.

For Rust core, CLI, or shared runtime semantic changes, run Rust formatting and tests, and add Python tests when behavior is exposed through the SDK.

For Rust changes, run cargo fmt --all, verify formatting with cargo fmt --all -- --check, and compile with cargo check --workspace --locked.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,py}

📄 CodeRabbit inference engine (.agents/skills/prepare-pr/SKILL.md)

For native binding changes, run cargo check -p fabric-python --locked.

Keep package names, import paths, and module names internally consistent, including the editable maturin build producing nemo_fabric._native and native artifacts being placed under python/src/nemo_fabric as expected by consumers.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

crates/fabric-core/**/*.{rs,py}

📄 CodeRabbit inference engine (.agents/skills/prepare-pr/SKILL.md)

Changes under crates/fabric-core must run both the Rust and Python test suites.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,rmeta}

📄 CodeRabbit inference engine (.agents/skills/validate-change/SKILL.md)

If Rust code changes, run cargo fmt --all -- --check and just test-rust.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

crates/fabric-core/**/*.rs

📄 CodeRabbit inference engine (.agents/skills/validate-change/SKILL.md)

If crates/fabric-core changes in a way exposed through Python, run both the Rust and Python suites.

For Rust API reference changes, update Rust documentation comments under crates/fabric-core/ instead of generated API reference files.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,py,pyi}

📄 CodeRabbit inference engine (.agents/skills/validate-change/SKILL.md)

**/*.{rs,py,pyi}: If public configuration types change, confirm schema snapshot tests in just test-rust pass and review generated schema diffs.
For schema or public contract changes, run both language suites and review changes under schemas/ and generated API references.

**/*.{rs,py,pyi}: Use snake_case for Rust and Python functions and variables; use PascalCase for Rust types and Python classes.
Run tests for every affected language surface. Changes touching the Rust core or public schemas require both Rust and Python test suites.
Use the existing style in the Python SDK, adapters, examples, and tests, and maintain synchronization between native Python binding declarations and Rust implementations.
If a change touches the Rust core or public schemas, run both just test-rust and just test-python; otherwise run the test targets for every affected language surface.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{py,pyi,rs}

📄 CodeRabbit inference engine (.agents/skills/validate-change/SKILL.md)

For Python SDK or PyO3 binding changes, use python-tests, run focused pytest tests first, then just test-python; rebuild with just build-python when native code or packaging changes.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,py,toml}

📄 CodeRabbit inference engine (.agents/skills/update-project-version/SKILL.md)

When editing version helpers, verify every nemo-fabric-* workspace package through Cargo metadata and reject a static version in python/pyproject.toml.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{toml,rs,py}

📄 CodeRabbit inference engine (.agents/skills/update-project-version/SKILL.md)

Avoid blind repository-wide replacement of version-like strings; distinguish package-version references from examples and unrelated dependency versions.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{md,mdx,yml,py,rs,sh}

📄 CodeRabbit inference engine (.agents/skills/review-doc-style/SKILL.md)

Keep documentation aligned with current NeMo Fabric behavior, repository layout, entry points, commands, package names, APIs, bindings, and support claims.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

**/*.{rs,py,pyi,json}

📄 CodeRabbit inference engine (CONTRIBUTING.md)

Public contract changes must keep checked-in JSON Schema snapshots and native Python binding declarations synchronized.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs
• typescript/adapter-contract/schemas/agent-run-result.schema.json
• schemas/adapter-contract/agent-run-result.schema.json

**/*.{rs,py,html,md,mdx,toml,yaml,yml,sh,bash}

📄 CodeRabbit inference engine (CONTRIBUTING.md)

All source files must include the appropriate SPDX copyright and Apache-2.0 license headers using the comment syntax for their file type; MDX files must use a JSX comment.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

crates/fabric-core/src/**/*.rs

⚙️ CodeRabbit configuration file

crates/fabric-core/src/**/*.rs: Review the Rust core for runtime lifecycle correctness, handle validation, capability routing accuracy, schema stability, and error semantics.
Public API changes should match committed schemas, tests, and documentation.

Files:

• crates/fabric-core/src/agent_execution.rs
• crates/fabric-core/src/schema.rs

schemas/**/*

⚙️ CodeRabbit configuration file

schemas/**/*: Schemas are generated public contract snapshots. Check that schema diffs correspond to intentional Rust type changes and are covered by core tests.

Files:

• schemas/adapter-contract/agent-run-result.schema.json

🧠 Learnings (2)

📚 Learning: 2026-08-07T07:15:33.918Z

Learnt from: AnuradhaKaruppiah
Repo: NVIDIA/NeMo-Fabric PR: 186
File: schemas/adapter-contract/legacy/adapter-invocation.schema.json:176-176
Timestamp: 2026-08-07T07:15:33.918Z
Learning: For the NeMo Fabric v1alpha southbound adapter contract, treat the adapter descriptor's `contract_version` as the version of the complete contract, including `RuntimeContext`. Keep `RuntimeContext` strict by rejecting unknown properties, and require a negotiated contract-version change for additive shape changes.

Applied to files:

• schemas/adapter-contract/agent-run-result.schema.json

📚 Learning: 2026-08-07T07:15:35.305Z

Learnt from: AnuradhaKaruppiah
Repo: NVIDIA/NeMo-Fabric PR: 186
File: schemas/adapter-contract/agent-config.schema.json:374-381
Timestamp: 2026-08-07T07:15:35.305Z
Learning: For the NeMo Fabric southbound adapter contract schemas, treat `AdapterDescriptor.contract_version` as the single negotiated version for the entire contract, covering `AgentConfig`, `AgentRunRequest`, `AgentRunResult`, and `RuntimeContext` before adapter startup. Do not require individual version fields in these payloads; verify behavior against the maintained adapter-contract README.

Applied to files:

• schemas/adapter-contract/agent-run-result.schema.json

🔇 Additional comments (5)

typescript/adapter-contract/schemas/agent-run-result.schema.json (1)

202-205: LGTM!

typescript/adapter-contract/scripts/projection-guards.mjs (1)

22-22: LGTM!

typescript/adapter-contract/scripts/generate.mjs (1)

285-288: LGTM!

typescript/adapter-contract/test/execution.test.ts (1)

22-22: LGTM!

crates/fabric-core/src/agent_execution.rs (1)

242-242: 🗄️ Data Integrity & Integration

Keep the contract version unchanged for this preview schema.

AgentRunResult is outside the negotiated contract. A version bump is required only when the runtime promotes and enforces typed invoke results.

			> Likely an incorrect or invalid review comment.

[zhongxuanwang-nv]

/merge