claude
fa7453dd9f
Two fold-selector fieldtest findings on the --tap seam, RED-first. Skipped-tap note (#334): an explicit --tap plan replaces the record-all default entirely (C27: unbound is inert) but gave no runtime signal that unlisted declared taps went unbound — a forgotten tap surfaced only as a missing trace file. bind_tap_plan's unbound arm now emits the C14 benign note (aura: note: declared tap "<name>" unbound this run) per skipped tap, exit unaffected. No new carrier: the arm is only reachable when plan.default_named is None (an explicit plan) — under record-all it is structurally dead, so the default emits nothing. Emitted runner-side beside the existing eprintln registers; the runner->CLI print migration is #297. Undeclared-tap refusal (#333): --tap on a tap the blueprint does not declare was refused without naming the valid taps, forcing the author back into the blueprint JSON. TapPlanError::UnknownTap now carries the declared-tap roster and Display appends it, mirroring UnknownLabel's fold-roster idiom (C29: a refusal names the closed set it checks against). Decision minuted on #333 (refusal roster over a new introspect view). Rider (#335): the fold roster doc lines now state the summary-row timestamp — the accumulator folds (count/sum/mean/min/max) land one row at the last warm (contributing) value's ts, and last gains the same at-its-own-timestamp wording first already carried. The ratification record lands in the sibling ledger/glossary commit. closes #334 closes #333
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C27 — Declared taps: named measurement points bind sinks run-mode-aware
Guarantee. A blueprint may declare taps — named, pure output-side
declarations { name, from: {node, field} }, the output-side twin of input_roles
(C26). A tap names an interior producer's output field
without naming a sink, exactly as a Role names an abstract input without naming a
source. At compile the tap resolves — and, for an interior composite, hoists to
the root — through the same lowering remap edges and OutField re-exports use
(resolve_tap_wire, a flat_taps accumulator threaded through the lowering
recursion), landing in FlatGraph.taps as a FlatTap { name, node, field } whose
name survives compile and is load-bearing for by-name binding (like
SourceSpec.role, #275).
Binding is run-mode-aware: the run-mode-owning layer constructs a consumer at
a bound tap via FlatGraph::bind_tap, which takes a caller-built
Box<dyn Node> sink (so the engine keeps its aura-core-only production
dependency — it never constructs a domain sink type) and appends it plus an edge
before bootstrap. What consumes a tap is declared per run by a tap plan
(#283): a Named { label, params } subscription resolves against a layered
fold registry (core vocabulary record | count | sum | mean | min | max | first | last; growth is a new Rust entry, C25, injectable by higher layers
without a core edit), and Live(closure) is the single deliberately non-data
variant. Both declared-tap entry points — the single-run path (run_signal_r)
and the bare measurement path (run_measurement) — bind through one shared
wiring pair, so they cannot drift: record persists the full series at constant
memory through the trace store's streamed write path (env.trace_store()), folds
keep an O(1) accumulator and land one summary row at finalize, so the tap columns
surface through the same tooling the campaign path feeds; a sweep/reduce run
leaves taps unbound.
Forbids. A tap carrying a channel endpoint or effect in the serialized artefact
— recording policy is run-mode authority, not fragment-embedded (a fragment must
not drag its measurement decisions into every harness that embeds it; the tier
ontology, C20/C21). The engine
constructing a domain sink type (the aura-core-only wall — the sink is
caller-built). Order statistics (median, etc.) inside the graph — they stay
sink/analysis-side (C18); multi-instrument study
inputs stay harness/World tier.
Non-error. An unbound tap is inert, not a fault — unlike an unbound root
input role, which check_root_roles_bound rejects (C26):
observation is optional, a fed input is mandatory. A declared-but-unbound tap
compiles and runs, its producer evaluating and its output discarded (a no-out-edge
producer is a valid runnable sink — the Kahn sort emits it,
check_ports_connected gates only inputs).
Why. Observability must be expressible in a hand-authored blueprint — the measurement-shaped study computes in the graph and surfaces via taps, no throwaway Rust harness — while recording stays a run-mode decision, not a fragment-embedded effect. Taps are designed DCE-compatible (a bound tap is a natural DCE root, an unbound tap a dead declaration) but this contract does not depend on DCE: an unbound tap's sink is simply never constructed (build-time elision, which the engine already tolerates). (#282, 2026-07-18.)
Current state
The tap types are realized in aura-engine: the authoring-level Tap
(crates/aura-engine/src/blueprint.rs, the output-side twin of Role), the
compiled FlatTap { name, node, field } and the FlatGraph.taps field
(crates/aura-engine/src/harness.rs), and FlatGraph::bind_tap, which appends a
caller-built Box<dyn Node> sink plus an edge and raises a typed UndeclaredTap
on a tap the graph does not declare (duplicate detection across binds is the
caller's — the method keeps no cross-call state). Lowering resolves and hoists taps
via resolve_tap_wire and the flat_taps accumulator (blueprint.rs). The
subscription seam is aura-runner::tap_plan (#283): TapPlan/TapSubscription,
the layered FoldRegistry (each entry carries a doc line — the help surface
and the roster-enumerating refusal — plus a scalar-typed param schema; all core
entries are param-less today, the seam ships in every entry's build signature),
and the shared bind_tap_plan/BoundTaps pair called by both declared-tap entry
points, run_signal_r (aura-runner::member) and run_measurement
(aura-runner::measure) — both arms of the single CLI verb aura run, whose
repeatable --tap TAP=FOLD selector (#310) makes the Named selection
data-reachable: no flag keeps the record-all default, any flag replaces the
plan entirely (unlisted taps stay unbound/inert). The boundary is thereby
fixed in place: selecting a subscription is run-mode authority, exercised
by the run-mode owner — on the one-shot path the CLI invocation itself, a
projection exercising this contract's authority, not a second home for
intent under C25 — while adding a fold stays a Rust
entry (role 2). The campaign/document carrier, and the reconciliation of the
presentation-tap namespace (persist_taps) with declared taps it requires,
is deferred to the Measurement-reachable milestone (#312/#327, minuted on
#312). The record
consumer (aura-runner::tap_recorder::TapRecorder) holds the trace store's
streaming writer in-graph — initialize opens (deferred acquisition), eval
appends (Timestamp, Cell) (zero per-cycle heap, #77), finalize reports
exactly one terminal outcome; fold consumers (aura-std::TapFold) land one
summary row, stamped with the source value's own timestamp for first/last
(they pin a single source instant) and with the finalize timestamp for the
accumulator folds (count/sum/mean/min/max summarise a range and have
no single source instant; min/max deliberately do not carry the extremum's
timestamp — ratified as-is, #335); live closures run inline
(aura-std::TapLive). The sweep/reduce
path never calls bind_tap.
The chain-pruning benefit — a sweep paying zero for the study wires behind an unbound tap — is deferred to the future DCE cycle (C23); the mechanism ships now, verified sound.
See also
- C26 — the input-side twin (
input_roles);check_root_roles_bound, the mandatory-input counterpart - C23 — compilation/lowering and the deferred DCE cycle the tap design anticipates
- C18 — the trace store and registry the tap series feed; order statistics live sink-side
- C20, C21 — the tier ontology behind run-mode recording authority
- C8 — the node/sink contract (a no-out-edge producer as a valid runnable sink)