ADR 0008 — Trace options deferred or rejected in phase 1

Status: Accepted (2026-09-26)

Each line is an option that was considered for recorded per-test traces and left out of phase 1, with the measurement or reason that decided it.

• Module-value ldsfld probe: rejected. It found 0 sites in Debug builds: F# reads a module value through its get_x() getter there, and the method-entry probe on the getter already records it.
• Tracing Release builds: rejected. Release builds inline small functions across assemblies, so their entry probes never fire and a trace would silently miss code. The weaver refuses optimized assemblies and the project runs untraced.
• Process-level open() interposer: deferred. File reads are captured at their .NET call sites instead. The file census (test-prune-traces file-census) measures what that misses; the interposer is reconsidered only if the census shows a gap it would close.
• Profiler ReJIT weaving: deferred. It needs the CLR profiler slot, which the coverage profiler already occupies, so traces could not record in the same run as coverage.
• Per-field type ids: deferred until after TestPrune.Core splits a type's content hash, which is what a field-level id would join against.
• Database table tracing: deferred to phase 4 (through the Npgsql ActivitySource).
• *[<ExcludeFromCodeCoverage>] on the recorder: rejected.* It would also hide the recorder from this repository's own coverage ratchet. The recorder is instead copied into a traced app without its PDB, which keeps it out of the app's coverage report.
• Selection from traces: out of scope for phase 1. Phase 1 records and measures only; selection rules start in phase 2 in shadow mode.
• Tracing TestPrune.Trace.Tests: rejected. That suite builds and tests its own recorder, and a traced launch would replace that build with the weaver's bundled one, so the suite would test a different recorder. On the first dogfood run, 10 of its tests failed traced and the run overflowed. The shadow bin now refuses an app whose deps.json lists the recorder as a project, and the project runs untraced. The phase-1 bars cover TestPrune.Tests only.