fix(sycl): prevent cross-TU kernel identity collisions

[lusoris]

Summary

Prevent Intel Arc from linking a SpEED chroma host closure to the temporal device image by giving the two SYCL translation units distinct launcher identities. Restore the explicit integer_moment_sycl.cpp output-capture alias lost by the silent revert, and add a portable source-contract red cap for unique kernel names, fp64-free SpEED device regions, and explicit output captures.

Type

• fix — bug fix
• sycl / cuda / simd — backend-specific

Checklist

• Commits follow Conventional Commits and the commit is signed.
• Formatting, scoped clang-tidy, make verify-all, strict MkDocs, pre-commit, and pre-push gates are green locally.
• Unit tests pass: the complete CPU fast suite is 148/148.
• The Arc A380 source, moment, chroma, temporal, and singular parity set is 5/5 at the unchanged 1e-4 tolerance.
• GPU twins were reviewed; this repair changes only SYCL linker identity/capture boundaries and no arithmetic or public behavior contract.
• The new Python regression test carries the repository's fork-local license header; no production C/C++ source or header was added.
• This is not a breaking change.
• No new ADR is required: ADR-0220 and ADR-0214 already own the fp64-free and parity contracts; this PR repairs implementation defects.

Bug-status hygiene

• docs/state.md closes T-SYCL-SPEED-CHROMA-BOTH-SINGULAR-REGRESSED-2026-09-23 with current executable evidence. BUG-048 remains open until its other independently owned restoration sections land and are reverified on master.

Netflix golden-data gate

• No Netflix assertAlmostEqual(...) score was modified.
• No golden data, score snapshot, tolerance, or arithmetic expression was modified.

Cross-backend numerical results

Intel Arc A380 / oneAPI 2026.1.1 / Level Zero 1.17.39758+10
test_sycl_kernel_source_contract  PASS
test_sycl_float_moment_parity     PASS
test_sycl_speed_chroma_parity     PASS
test_sycl_speed_temporal_parity   PASS
test_sycl_speed_singular_parity   PASS
Result: 5/5 at the unchanged 1e-4 ADR-0214 tolerance

Deep-dive deliverables

• Research digest — docs/research/2090-sycl-silent-revert-residuals-2026-09-24.md.
• Decision matrix — the digest's ## Alternatives considered records the five evaluated options and selected minimum repair.
• AGENTS.md invariant note — core/src/feature/sycl/AGENTS.md documents unique SpEED launcher identities and explicit output captures.
• Reproducer / smoke-test command — pasted below.
• CHANGELOG fragment — changelog.d/fixed/sycl-silent-revert-residuals.md.
• Rebase note — docs/rebase-notes.md records the SYCL kernel-identity/capture invariant.

Reproducer

python3 core/test/test_sycl_kernel_source_contract.py -v

ONEAPI_DEVICE_SELECTOR=level_zero:gpu meson test -C build-sycl \
  test_sycl_speed_chroma_parity test_sycl_speed_temporal_parity \
  test_sycl_speed_singular_parity test_sycl_float_moment_parity \
  test_sycl_kernel_source_contract --print-errorlogs

Validation

• Exact base: 4e6916d16ac57647105d14a47a6680117d6b5738.
• Before the fix, the Arc singular red cap reproduced a NaN and object inspection found two intersecting generated kernel tags; rebuilt objects have zero intersections.
• Arc A380 focused suite: 5/5 passed at unchanged 1e-4.
• Complete CPU fast suite: 148/148 passed.
• All three touched SYCL translation units: zero file-local clang-tidy diagnostics with the fresh oneAPI compilation database.
• make verify-all, strict MkDocs, full changed-file pre-commit, state/changelog checks, and silent-revert checks passed.
• Writable AGY normal-mode review completed naturally with PASS and no remaining edits.

Surface opt-outs

no docs needed: internal SYCL kernel identity and capture repair with no user-discoverable surface change.

no ffmpeg-patches update needed: no public header, C API, CLI flag, Meson option, pkg-config surface, or shipped FFmpeg integration changed.

Known follow-ups

No performance tuning, tolerance adjustment, retraining, or unrelated BUG-048 restoration is part of this PR.