[eiriktsarpalis]

Generated object readers currently allocate a string for every JSON property name before dispatching. This removes those temporary allocations by matching unescaped UTF-8 spans directly.

Approach

• Borrow contiguous, unescaped reader input; use Utf8JsonReader.CopyString() with stack or pooled buffers for escaped and segmented names, preserving invalid-text validation.
• Generate length and discriminating-byte patterns followed by UTF-8 literal SequenceEqual checks. Full byte-list patterns did not receive equivalent wide-comparison optimizations in the inspected ARM64 code.
• Omit per-reader rental state when every known name's maximum escaped representation fits the stack buffer. Oversized unknown names still undergo validation.
• Add regression coverage for escaping, Unicode, segmented input, invalid text, allocations, and stack-buffer boundaries; refresh Debug and Release snapshots.

Performance

Refresh all 99 measurements, eight charts, and the exported dataset in the performance documentation. Fast-path allocations fall from 576 B to 440 B for the small POCO, from 3.06 KiB to 2.02 KiB for the large POCO, and from 10.80 MiB to 5.73 MiB for the CITM batch.

Separate lookup experiments favored generated UTF-8 dispatch over full byte-list patterns and frozen character/byte alternate lookups for the measured four- and 24-property schemas. Scratch benchmarks are not included in this PR.

Validation

• Full make test: CLR and Native AOT suites passed.
• Debug and Release generated-source snapshots passed.
• All nine JSON fixtures passed serializer-output and round-trip validation; all 99 benchmarks completed using six warmups and twelve measurement iterations.
• Chart-generation checks and git diff --check passed.

[codecov]

Codecov Report

❌ Patch coverage is 97.72727% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.47%. Comparing base (429bae8) to head (3f8a4a1).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../PolyType.FastPathJson/Converters/ScalarHelpers.cs	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #554      +/-   ##
==========================================
+ Coverage   94.46%   94.47%   +0.01%     
==========================================
  Files         299      299              
  Lines       19556    19637      +81     
  Branches     3820     3797      -23     
==========================================
+ Hits        18473    18553      +80     
  Misses        795      795              
- Partials      288      289       +1     

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