tests: cover duplicate json keys

Author: adz

.gitignore

@@ -31,6 +31,7 @@ benchmarks/CodecMapper/
 
 # Build and temp
 .gemini/
+.artifacts/
 .DS_Store
 *.log
 output/

TASKS.md

@@ -31,3 +31,11 @@ Completed rename, parser, bridge, compatibility, JSON Schema, docs, and projecti
 - [x] **Task 35: Add property-based test coverage for codec laws**
   - Added `FsCheck.Xunit`-backed round-trip properties in `tests/CodecMapper.Tests` for representative nested-record, option, and collection schemas across both JSON and XML.
   - Kept the generators inside the supported deterministic surface so failures stay debuggable and align with the library's intentional JSON/XML subset.
+
+- [x] **Task 36: Add repeatable profiling workflow for benchmark hot paths**
+  - Add a repo-local profiling harness around the benchmark runner so CPU and allocation investigations are repeatable instead of one-off terminal sessions.
+  - Prefer local tooling that exists on the machine today; `perf` is available, while `dotnet-trace` and `dotnet-counters` are not.
+  - First slice landed: the benchmark runner now has a focused `profile` mode, and `scripts/profile-benchmark-hot-path.sh` captures `perf stat`, `perf.data`, injected JIT symbols, and a text report under `.artifacts/profiling/`.
+  - Capture at least one checked-in workflow for JSON serialize and deserialize hot paths, with outputs that can be inspected as call stacks or folded into flamegraphs.
+  - Keep the profiling entry points deterministic and parameterized so later optimization work can compare the same workload before and after changes.
+  - Document how to rerun the profiling workflow and where generated artifacts land so it becomes part of normal performance work, not tribal knowledge.

src/CodecMapper/Json.fs

@@ -1380,8 +1380,7 @@ module Json =
     ///
     /// Inline schema pipelines read more clearly when the final `build` and
     /// JSON compile step collapse into one terminal pipeline stage.
-    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> =
-        builder |> Schema.build |> compile
+    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> = builder |> Schema.build |> compile
 
     ///
     /// `codec` remains as the shorter schema-to-codec alias for callers that

src/CodecMapper/KeyValue.fs

@@ -306,8 +306,7 @@ module KeyValue =
     ///
     /// Inline schema pipelines read more clearly when the final `build` and
     /// key/value compile step collapse into one terminal pipeline stage.
-    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> =
-        builder |> Schema.build |> compile
+    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> = builder |> Schema.build |> compile
 
     ///
     /// `codec` remains as the shorter schema-to-codec alias for callers that

src/CodecMapper/Xml.fs

@@ -721,8 +721,7 @@ module Xml =
     ///
     /// Inline schema pipelines read more clearly when the final `build` and
     /// XML compile step collapse into one terminal pipeline stage.
-    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> =
-        builder |> Schema.build |> compile
+    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> = builder |> Schema.build |> compile
 
     ///
     /// `codec` mirrors `Json.codec` for callers that still prefer the direct

src/CodecMapper/Yaml.fs

@@ -382,8 +382,7 @@ module Yaml =
     ///
     /// Inline schema pipelines read more clearly when the final `build` and
     /// YAML compile step collapse into one terminal pipeline stage.
-    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> =
-        builder |> Schema.build |> compile
+    let inline buildAndCompile (builder: Builder<'T, 'T>) : Codec<'T> = builder |> Schema.build |> compile
 
     ///
     /// `codec` mirrors the other format modules for callers that still prefer

tests/CodecMapper.Tests/JsonParserTests.fs

@@ -110,6 +110,11 @@ let ``Skip unknown fields with escaped quotes and backslashes deterministically`
     let value = Json.deserialize idCodec json
     test <@ value = { Id = 42 } @>
 
+[<Fact>]
+let ``Duplicate object keys keep the last known value`` () =
+    let value = Json.deserialize idCodec """{"id":1,"id":42}"""
+    test <@ value = { Id = 42 } @>
+
 [<Fact>]
 let ``Reject missing required keys`` () =
     expectFailure "JSON decode error at $.id: Missing required key 'id'" (fun () -> Json.deserialize idCodec "{}")