claude
fd303de94d
All 14 process::exit sites in aura-runner (member x8, measure x5,
translate x1) convert to RunnerError { exit_code, message } propagation;
run_signal_r / run_measurement return Result tuples carrying the
skipped-tap names beside the C18 reports (record shapes untouched), and
the CLI owns printing via the shared exit_on_runner_error arm (the
dispatch_reproduce pattern — reproduce now uses the same helper).
cost_knob becomes fallible: the sweep worker maps it into the cell's
MemberFault (closing the one hole in 'a worker never process-exits'),
the persist path keeps its string channel. The skipped-tap note is
CLI-printed from returned data, byte-identical.
The one deliberate behaviour change is the minuted C14 adjudication:
refusals in the content of what argv named (binding, synthetic mismatch,
compile, tap-bind content, exposes-neither) move exit 1 -> 2; the
boundary is FORM vs VALUE — an out-of-domain override value keeps the
runtime class via the panic containment, matching the campaign leg.
Environment/data/IO refusals stay 1 (TapPlanError::exit_class is the
single source). Named re-pins in exec.rs, run_refuses_unrunnable_
blueprint.rs, tap_recording.rs, graph_construct.rs; new library-level
test pins the milestone promise (a refusal returns in-process, the
embedding host survives). Prose is byte-identical everywhere.
Docs in lockstep: C28 deferred block closed (14 sites, hole closed),
C14 partition + form-vs-value boundary, C27 note emission, guide exit
classes. Fork minutes: issues/297#issuecomment-4868 and -4873.
closes #297
8.1 KiB
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). The CLI surfaces this to the human
as a note (aura: note: declared tap "…" unbound this run) printed from the
unbound names the entry points return beside their report — never emitted by
the library itself (#297).
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 exec (#319),
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). BoundTaps carries the
unbound tap names out (skipped: Vec<String>), riding beside the returned
report rather than inside it, so the CLI — not the library — prints the
unbound-tap note (#297). 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, emitted at finalize and stamped with the instant of the last
contributing (warm) value — first alone pins the first contributing
instant; min/max deliberately do not carry the extremum's timestamp (a
whole-window row privileges no interior instant) — 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.
#337 (2026-07-26 harvest) ships the positive discovery view:
Composite::declared_taps() (crates/aura-engine/src/blueprint.rs) walks the
blueprint depth-first collecting (tap name, source wire, column kind), bare
at every depth, bounds-total over an invalid wire; graph introspect --taps <FILE|ID> renders one row per declared tap (a tap-less blueprint is a
stderr-noted listing, exit 0). This closes the recovery-only discovery
gap: before #337, the only way to learn a blueprint's declared tap names was
provoking bind_tap_plan's UnknownTap refusal roster (#333) — a real name
surfaced only as the side effect of naming a wrong one first. The refusal
roster itself is unchanged and remains the recovery half (what to do once
a tap name is already wrong); --taps is the discovery half (learning the
right names up front).
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)