Declared taps (C27, #282) were authorable only by hand-patching the raw
blueprint envelope's `taps` array, where `node` is a raw interior index —
an index miscount was the expected mistake and the root friction behind the
two `aura run` panics the measurement-milestone fieldtest found.
Add a `tap` op to the construction op-script vocabulary — the exact
output-side twin of `expose`. It names its source wire by the dotted
`"node.field"` identifier the op surface uses everywhere (`split_port` +
`resolve_output_field` + `node_index`), so
`{"op":"tap","from":"fast.value","as":"fast_ma"}` replaces patching
`{"node":14,"field":0}`.
Engine (construction.rs): `Op::Tap`, its `tap()` handler (a verbatim twin
of `expose` — same resolvers, same name-dedup, appending a `Tap` to a new
`taps`/`tap_names` namespace), and `OpError::DuplicateTap` (the twin of
`DuplicateOutput`, stricter than the raw envelope, which enforces no
tap-name uniqueness). `finish()` now threads `.with_taps(self.taps)` into
the built `Composite` — fixing a latent drop #282 left (it built
`.with_gangs` but never `.with_taps`, so op-built composites silently lost
their taps).
CLI (graph_construct.rs): `OpDoc::Tap` (externally tagged, `"as"`-renamed
like `expose`) + the `kind_label` / `From` / `format_op_error` arms (the
last compiler-enumerated by the exhaustive match).
No change to the `Tap` / `FlatTap` / `bind_tap` / `aura run` machinery — the
op-declared tap flows through the existing #282 compile + record path
unchanged.
Verification: 7 new tests green (4 engine: resolve+append, bad-port /
ghost-node refusal, duplicate-name refusal, finish-threads-into-FlatGraph;
1 CLI serde round-trip; 2 CLI E2E over the real `aura graph build` /
`aura run` subprocess — one pinning the exact serialized
`"taps":[{"name":"fast_ma","from":{"node":0,"field":0}}]`, one proving an
op-authored tap round-trips through build -> run -> persisted trace). Full
workspace suite green; clippy clean.
The RED-before-GREEN step was verified by a temporary stash of the
production edits (the `Tap` / `with_taps` machinery pre-existed from #282,
so a fresh RED-only test could not be authored) — the new tests fail
without the edits, pass with them.
Docs (the authoring-guide `tap` row, the ledger op-list `tap` line, and a
worked tap-authoring example) are deliberately out of this commit's scope —
they land in #285, the docs follow-up in this same cycle.
closes#284
claude
43a1cc44d3