AG-UI .NET SDK Code Review

Encodes the AG-UI .NET SDK's house rules so a reviewer flags real violations a generic C# reviewer misses. Authoritative sources: sdks/dotnet/AGENTS.md (house rules) and sdks/dotnet/docs/architecture.md (design boundaries). Each rule cites a real enforcement example in the repo; full BAD→GOOD examples and per-rule exceptions live in references/rules.md. The change-footprint and test rules below distil the minimize-change-footprint, ensure-test-coverage, and ensure-test-quality review conventions for this SDK.

Reviewer discipline

• High signal-to-noise. Only flag a genuine violation of a rule below, tied to its cited convention. Don't invent nits or restate analyzer output.
• Verify before flagging. Read the actual changed code and confirm the rule applies. Automated reviewers have high false-positive rates.
• Scope. Review only files under sdks/dotnet/. Skip generic style already enforced by TreatWarningsAsErrors, nullable, and EditorConfig.
• Blast radius. Fix nothing — this skill only reports. Local convention violations get a finding; codebase-wide concerns are noted as out-of-scope follow-ups, not per-line nits.
• Severity: ❌ must fix (breaks AOT/wire/build/boundary); ⚠️ should fix (convention drift); 💡 optional polish.

The review process

Step 0 — Ground truth & file classification. Derive the package map from AGUI.slnx; skim AGENTS.md + docs/architecture.md. Classify each changed file: production | test | sample | proto | csproj | public-api | docs. Rules are gated by class.

Step 1 — Determine and summarize the change set. Resolve what is under review, in order: an explicit target (PR number / branch / commit range); else the current branch vs. its tracking/base branch (git merge-base <base> HEAD); plus staged, unstaged, and untracked working-tree changes. Then write a short summary of what the diff does — new types, wire/protocol changes, public-surface changes, new dependencies, src-vs-sample placement. This frames every phase and catches scope creep early.

Step 2 — Walk the rules, phase by phase (A→G). For each phase, check every applicable changed file against every rule in that phase. Write each finding immediately: file:line, rule ID, severity, one-line fix. Verify the code first.

Step 3 — Self-validation. Dedupe; confirm each finding cites a real rule and a real line; confirm no rule was applied to the wrong file class; drop anything not verifiable in the actual diff.

Step 4 — Emit the review summary (see below) — a single human-readable comment, findings grouped by severity with a verdict and coverage line.

Phase A — Scope / scenarios

• NET-SCOPE-01 Every change traces to a spec requirement or issue [⚠️]
• NET-SCOPE-02 No unrequested capability, configurability, or dependency [⚠️]
• NET-SCOPE-03 A wire/protocol change carries compatibility coverage [❌]
• NET-SCOPE-04 Sample-only behavior stays out of src/ [⚠️]
• NET-SCOPE-05 Minimal footprint — every diff line serves the task; no unrelated refactor, speculative abstraction, or cosmetic churn [⚠️]

Phase B — Design / architecture

From docs/architecture.md "Architectural constraints".

• NET-ARCH-01 No src/ project references Microsoft.AspNetCore.App [❌] — git grep "Microsoft.AspNetCore" -- sdks/dotnet/src must be empty.
• NET-ARCH-02 Correct package placement (wire→Abstractions, SSE→Formatting, proto→Protobuf, client/transport→Client, hosting→Server) [❌]
• NET-ARCH-03 Dependency direction — Client and Server never reference each other [❌]. Cite: src/AGUI.Server/AGUI.Server.csproj.
• NET-ARCH-04 IChatClient is the only integration point — no bespoke agent abstraction [💡]
• NET-ARCH-05 Every type has a single reason to change [⚠️]
• NET-ARCH-06 No interface without multiple implementations or a test-double need [⚠️]
• NET-ARCH-07 Make invalid states unrepresentable (enums/types over bool/string) [⚠️]
• NET-ARCH-08 One class per file; file name matches the type [⚠️]

Phase C — Implementation / correctness

From AGENTS.md "JSON serialization" / "Code style".

• NET-IMPL-01 Every serializable type registered in AGUIJsonSerializerContext via [JsonSerializable(typeof(T))] [❌]. Cite: src/AGUI.Abstractions/Serialization/AGUIJsonSerializerContext.cs.
• NET-IMPL-02 No JsonSerializer.Serialize<object> and no reflection-based serialization — go through the source-gen context [❌]
• NET-IMPL-03 Polymorphic JSON uses a hand-written discriminator JsonConverter<T> [❌]. Cite: src/AGUI.Abstractions/Events/BaseEventJsonConverter.cs.
• NET-IMPL-04 Property attribute kit present: explicit [JsonPropertyName], [JsonIgnore(WhenWritingNull)] on optionals, required strings = string.Empty, collections = [] [⚠️]. Cite: src/AGUI.Abstractions/Events/RunStartedEvent.cs.
• NET-IMPL-05 ConfigureAwait(false) on every await in src/ [⚠️]. Cite: src/AGUI.Client/AGUIChatClient.cs.
• NET-IMPL-06 [EnumeratorCancellation] on the token of any IAsyncEnumerable<T> method [⚠️]. Cite: src/AGUI.Formatting/SseEventStreamFormatter.cs.
• NET-IMPL-07 ArgumentNullException.ThrowIfNull(...) for public-API argument validation [⚠️]
• NET-IMPL-08 Validate external input at the boundary, not deep in the stack [⚠️]
• NET-IMPL-09 Guard every code path — no silent default/fallthrough [⚠️]
• NET-IMPL-10 No swallowed exceptions (empty or log-only catch) [⚠️]
• NET-IMPL-11 Never log or expose sensitive data in errors [❌]
• NET-IMPL-12 No dead, commented-out, or impossible-condition defensive code [⚠️]
• NET-IMPL-13 No logic duplicated across the changeset — extract a shared helper at 3+ uses (Rule of Three; don't extract for 1–2) [⚠️]
• NET-IMPL-14 Prefer BCL/platform APIs over hand-rolled equivalents [⚠️] — exception: deliberate AOT-safe hand-written paths (the JsonElement↔Value bridge, the discriminator converters) are intentional, not violations.

Phase D — Wire compatibility

• NET-WIRE-01 Protocol types match the TS reference — honor the // Keep in sync with sdks/typescript/... markers [❌]. Cite: src/AGUI.Abstractions/Events/RunStartedEvent.cs.
• NET-WIRE-02 Events are additive — unknown types round-trip via RawEvent; don't remove or repurpose existing fields [⚠️]
• NET-WIRE-03 Protobuf parity preserved for the supported event set [❌]

Phase E — PublicAPI analyzer

• NET-API-01 Any public-surface change updates that project's PublicAPI.Unshipped.txt (build fails RS0016 otherwise) [❌]. Cite: sdks/dotnet/Directory.Build.targets, src/AGUI.Abstractions/PublicAPI.Unshipped.txt.
• NET-API-02 A new event type completes the full checklist (class in Events/ deriving BaseEvent; Type → AGUIEventTypes constant; [JsonSerializable]; read case in BaseEventJsonConverter; PublicAPI.Unshipped.txt; round-trip test) [⚠️]

Phase F — Style / naming

From AGENTS.md "Code style" / "Naming" (not all analyzer-enforced).

• NET-STYLE-01 sealed on every non-abstract class [⚠️]
• NET-STYLE-02 No record types — use sealed class with properties [❌]
• NET-STYLE-03 No tuples in public APIs — define a named type [⚠️]
• NET-STYLE-04 Braces always on if/for/foreach/while [⚠️]
• NET-STYLE-05 Naming: events {Name}Event; discriminators SCREAMING_SNAKE_CASE constants in AGUIEventTypes; outcome/role constants lowercase (never enums); options AGUI{Purpose}Options; extensions {Target}Extensions; tests {TypeUnderTest}Test [⚠️]
• NET-STYLE-06 DI-extension types use the Microsoft.Extensions.DependencyInjection namespace; all other types use the project RootNamespace with no sub-namespaces [⚠️]
• NET-STYLE-07 No XML docs (///) on internal/private members [⚠️]
• NET-STYLE-08 Don't reformat code you didn't otherwise change [⚠️]

Phase G — Tests

From AGENTS.md "Running tests"; coverage/quality rules distilled from ensure-test-coverage and ensure-test-quality.

SDK-specific:

• NET-TEST-01 Serialization tests assert concrete JSON property names via JsonDocument — not via the deserialized object [⚠️]
• NET-TEST-02 No full-JSON-string comparisons — assert individual properties [❌]
• NET-TEST-03 No reflection to enumerate types or verify membership [❌]
• NET-TEST-04 Wire-affecting change ⇒ compatibility fixture + round-trip in tests/AGUI.Abstractions.UnitTests/Compatibility/ [⚠️]
• NET-TEST-05 New public behavior ⇒ unit test; server-pipeline change ⇒ integration test (tests/AGUI.Hosting.AspNetCore.IntegrationTests/) [⚠️/💡]

Coverage:

• NET-TEST-06 A new/changed class with branching logic has a test covering happy path, primary error path, and boundary values (null/empty/zero/single) [⚠️]
• NET-TEST-07 Don't test trivial code — DTOs/records with no logic, one-line delegations, constant returns [💡]
• NET-TEST-08 Test through DI + InternalsVisibleTo, not members made public for tests [⚠️]

Quality:

• NET-TEST-09 Every test asserts a specific observable value — no assertion-free tests, no bare Assert.NotNull/True/NotEmpty standing in for the real value [❌]
• NET-TEST-10 Deterministic and isolated — no Thread.Sleep/Task.Delay for synchronization, no execution-order dependence, side effects cleaned up (files/ports/env) [❌]
• NET-TEST-11 Test behavior, not implementation — prefer hand-written fakes over mock.Verify(Times.*) (unless the call count is the spec'd behavior); [Theory] for data variation, [Fact] for behavior; AAA visible inline with factory helpers (not shared mutable fixtures) below the tests; no // TODO or empty test bodies [⚠️]

Self-validation

• The change set was resolved (target / tracking branch / working tree) and summarized
• Every applicable changed file was walked against every phase's rules
• Each finding cites a real rule ID, file, and line, and was verified in the diff
• No rule applied to the wrong file class; no duplicates
• Clean diffs are reported as clean — no padding

Common pitfalls

Review summary

Produce a single human-readable Markdown comment — a reviewer's summary the author can read top to bottom. Lead with the verdict, then the findings grouped by severity (most severe first), each one self-contained.

## AG-UI .NET SDK code review

**Verdict:** <Request changes | Comment | Looks good> — <one-sentence reason>
**Change set:** <branch vs base, e.g. `feat/x` vs `main`> · <N files reviewed>
(+<U untracked>) · **Findings:** ❌ <a> · ⚠️ <b> · 💡 <c>

<One short paragraph: what the change does and the overall read.>

### ❌ Must fix
- **`src/AGUI.Abstractions/Events/FooEvent.cs:42`** · `NET-IMPL-01` — new event type
  isn't registered in `AGUIJsonSerializerContext`; it fails under AOT.
  **Fix:** add `[JsonSerializable(typeof(FooEvent))]`.

### ⚠️ Should fix
- **`src/AGUI.Client/AGUIChatClient.cs:88`** · `NET-IMPL-05` — bare `await` in
  library code. **Fix:** append `.ConfigureAwait(false)`.

### 💡 Optional
- **`src/AGUI.Server/StreamAdapter.cs:17`** · `NET-ARCH-04` — bespoke agent
  abstraction; the SDK integrates via `IChatClient`. **Fix:** drop the wrapper.

### Coverage
Phases checked: A–G. No findings in: **B Design**, **D Wire**, **E PublicAPI**.

Rules for the summary:

• Order findings by severity (❌ → ⚠️ → 💡), then by file. One bullet per finding: bold file:line, the RULE-ID, a plain-language description, and an italic Fix: with a one-line remedy. The reader can look the ID up in references/rules.md.
• Omit empty severity sections. Always include the Coverage line so the author sees which phases were clean versus untouched.
• Clean diff: skip the severity sections and write a single line — ✅ No violations of the AG-UI .NET house rules — checked phases A–G across N files.
• Verdict mapping: any ❌ → Request changes; only ⚠️/💡 → Comment; none → Looks good. The skill never approves or blocks automatically — the verdict is advisory and the author decides.