cnc_wams/wasm-port/docs/drift-report.md

# Drift Report

## Current Status

As of the current upstream baseline, no byte-level drift is allowed between
files listed in `tools/source-manifest.txt` and the matching files under
`../linuxcnc/`.

The enforced upstream baseline is:

```text
60597ee0718873d2449058c824262a275e5e4bad
```

`tools/verify_vendor_sync.sh` enforces this by comparing every manifest file
against upstream during native validation.

## Allowed Standalone Boundaries

The following differences are intentional runtime boundaries, not LinuxCNC
semantic rewrites:

| Boundary | Standalone treatment |
| --- | --- |
| RTAPI | Minimal compatibility shim in `runtime/core/shims/rtapi.h`. |
| HAL lookup | Standalone HAL adapter for `_hal[...]` named parameter reads. |
| INI lookup | Standalone INI adapter around vendored LinuxCNC INI parser behavior. |
| Canonical output | Canonical calls are captured as test events instead of driving hardware. |
| Feed-rate state | `SET_FEED_RATE` updates standalone canonical runtime state so vendored `convert_length_units()` can read it back through `GET_EXTERNAL_FEED_RATE()` during G20/G21 changes. |
| Tool-data reload | LinuxCNC `RELOAD_TOOLDATA` is captured as a canonical test event; browser/native tool-table reload plumbing remains a future host/runtime adapter. |
| Tool table storage | Vendored LinuxCNC `tooldata_common.cc` owns tool-table parsing and formatting; the standalone boundary only supplies the in-memory `tooldata_get()`/`tooldata_put()` callbacks, exposes load/save through the WASM C ABI, and forwards the host random-toolchanger flag to LinuxCNC `tooldata_init()`. |
| Tool slot status | Standalone tool adapter state supplies `GET_EXTERNAL_TOOL_SLOT()` and `GET_EXTERNAL_SELECTED_TOOL_SLOT()` for vendored `Interp::synch()`; `linuxcnc_interp_init_harness` guards current/selected slot synchronization. |
| Interpreter state tags | LinuxCNC `UPDATE_TAG` callbacks are captured from the state tags packed by vendored interpreter code; standalone code does not derive modal state. |
| Rotary indexer lock state | LinuxCNC `UNLOCK_ROTARY` and `LOCK_ROTARY` callbacks are captured from the vendored single-axis indexer path; standalone code does not implement rotary-indexing semantics. |
| File flush | LinuxCNC `FINISH` is captured as a canonical test event on the vendored `%`-delimited file-reading path. |
| WASM parameter-file backup | LinuxCNC `save_parameters()` calls `link()` to create the `.bak` parameter-file backup; `runtime/core/linuxcnc_wrap/linuxcnc_wasm_posix_stubs.cpp` maps that WASM/MEMFS edge to a file copy so the vendored save path can run unchanged. |
| Interpreter reset | LinuxCNC `ON_RESET` is captured as a canonical test event on the vendored interpreter reset/file-open path. |
| Interpreter init | LinuxCNC `INIT_CANON` and the canonical initialization sequence from vendored `Interp::init()` are captured as test events. |
| Comment logging | LinuxCNC `LOGOPEN`, `LOG`, `LOGAPPEND`, and `LOGCLOSE` callbacks are captured as canonical test events instead of writing host log files. |
| EMC status machine units | A narrow standalone `emcStatus` shim exposes the machine-units field used by vendored interpreter conversion and initialization code; `linuxcnc_emc_status_probe` and `linuxcnc_interp_init_harness` guard the inch/mm boundary. |
| Python/remap | Python/remap hooks are stubbed at the runtime edge. |
| Dynamic interpreter path | `interp_base.cc` probe uses standalone `EMC2_HOME` compile-time path boundary. |
| Realtime scheduler | TP probes seed deterministic status/config data instead of running LinuxCNC realtime process topology. |
| Kinematics component lifecycle | Kinematics modules are initialized through LinuxCNC module entry points where native runtime probes exist, while HAL component init/ready/exit, HAL pin allocation, and RTAPI module metadata are handled by standalone shims. |
| Go math C/C++ linkage | `genserkins` runtime probing compiles vendored `gomath.c` through a narrow C++ wrapper so LinuxCNC `genserfuncs.c` can link to the upstream Go math symbols without editing vendored source. |
| Switchkins iterative forward | `genhexkins` runtime probing follows LinuxCNC switchkins iterative-forward behavior, including the first-call warmup path before asserting roundtrip convergence. |
| Browser storage | OPFS remains outside the native core; `runtime/opfs/file-service.js` owns browser text-file persistence, `runtime/opfs/path-model.js` owns host-side storage paths for INI, tool table, parameter, G-code, preview-cache, and session-snapshot content, `runtime/opfs/snapshot-store.js` owns generic JSON session snapshot persistence, `runtime/opfs/machine-file-store.js` owns pure-text machine-file and G-code persistence, `runtime/opfs/linuxcnc-parameter-bridge.js` only copies parameter files between OPFS text storage and the LinuxCNC-backed WASM parameter-file ABI, `runtime/opfs/linuxcnc-tool-table-bridge.js` only copies tool tables between OPFS text storage and the LinuxCNC-backed WASM tool-table ABI, and `runtime/opfs/linuxcnc-machine-session-bridge.js` groups INI, parameter, and tool-table loading without interpreting their CNC semantics. |

## Enforced Non-Drift Rules

- Do not edit `../linuxcnc/`.
- Do not patch vendored files without adding a patch under `patches/` and
  documenting the reason.
- Do not add standalone `Interp::...` member definitions outside the
  documented Python/remap runtime-edge stubs.
- Do not add `.c` or `.cc` manifest files without a source compile probe.
- Do not sync from a different upstream commit without updating
  `tools/upstream-baseline.txt` and `docs/scope-and-baseline.md`.

## Known Gaps

- No browser/full-core WASM parity tests yet. The INI parser now has Node and
  Chromium smoke harnesses against vendored LinuxCNC `inifile.cc`.
- JS SDK validation now covers the INI WASM wrapper around vendored LinuxCNC
  `inifile.cc` and the interpreter-core SDK wrapper around the existing
  exported C ABI. The interpreter SDK only manages strings, Emscripten file
  writes, and calls into vendored LinuxCNC execution paths, including
  parameter-file restore/save and tool-table load/save.
- OPFS validation covers a Node mock of the file-service adapter, the
  host-side path model, generic session snapshot storage, pure-text machine
  file and G-code storage, parameter/tool-table bridge copying into the
  interpreter SDK filesystem, grouped machine-session loading, and a Chromium
  localhost round trip for those persistence paths.
- Host-side smoke validation is aggregated by
  `tests/host/verify_host_smokes.sh` so Node, WASM, OPFS, and browser checks
  run from one command.
- Identity/trivial, `5axiskins`, TRT `xyzac`/`xyzbc`, delta, SCARA, PUMA,
  serial, hexapod, pentapod, and related kinematics sources now have native
  source-probe coverage.
- Full machine baselines beyond the current identity/trivial, `5axiskins`,
  TRT, delta, SCARA, PUMA, serial `genserkins`, hexapod `genhexkins`,
  pentapod `pentakins`, and other existing runtime probes are not established.
- Positive cutter-compensated motion and cutter compensation rejection paths
  now have standalone interpreter fixture coverage through vendored LinuxCNC
  source.
- Fixture expectations are checked against the standalone vendored source
  path. The upstream `rs274` side-by-side baseline now covers simple motion,
  arc geometry, offsets, feed-control, comment/logging, numbered-parameter,
  probing, spindle-orient, file-open reset, file-finish, tool-reload, and
  tool select/change/length-offset, canned-cycle, state-tag motion, tool-table
  setup, and O-word subroutine fixtures; it also covers threading/rigid tap,
  NURBS dispatch boundaries, and comparable canonical runtime edge and
  program-end cleanup calls.
  Adapter-heavy fixtures, standalone modal-state assertions, and upstream
  `rs274` output gaps such as `WAIT` or hidden NURBS control-point detail still
  need dedicated native LinuxCNC baselines.
- `canned_cycles` is now in the upstream `rs274` side-by-side baseline after
  the minimal interpreter harness was aligned with LinuxCNC `Interp::init()`
  default `G73/G83` peck-clearance values for millimeter units.
- `tool_table_setup` is now in the upstream `rs274` side-by-side baseline using
  a dedicated `rs274 -t` tool table and `-i` millimeter-unit INI boundary.
- `tool_semantics` now compares its T/M6/G43/G49 canonical subset with
  upstream `rs274 -t -i`; M61 current-pocket host-state behavior remains a
  standalone fixture expectation.

## Current Drift Conclusion

Within the native extracted-core scope, the port currently has no permitted
byte-level drift from vendored LinuxCNC source files. All current behavior
coverage is guarded by upstream baseline validation, vendor sync validation,
source compile probes, native harnesses, and fixture checks.