feat(engine): bind ingestion sources by role key — SourceSpec.role + bind_sources/run_bound

refs #275

The engine-side half of by-name source binding. `SourceSpec` carries a load-bearing
`role: Option<String>` — `Some(name)` for a spec lowered from a bound `Role` (carried
through the blueprint lowering, previously dropped at compile), `None` for a
hand-built raw-index spec. A pure `bind_sources(specs, keyed_supply)` resolves a
`Vec<(role, Box<dyn Source>)>` into the positional `Vec` `run` consumes, in
`SourceSpec` declaration order, erroring named (`SourceBindError`:
Missing/Extra/Duplicate/Unnamed feed) on a mis-bind. `Harness::run_bound` is the
ergonomic method the by-name production path calls.

The raw-index `run(Vec)` primitive and the k-way merge / per-cycle event loop are
untouched: a positional run stays byte-identical (C1, pinned by
`run_bound_out_of_order_matches_positional_run`), and every existing `run(Vec)` caller
keeps working (it ignores `role`). A `BTreeMap` index makes the Duplicate/Extra
diagnostics deterministic.

C4's tie-break guarantee ("source declaration order") is unchanged — `bind_sources`
emits in `SourceSpec` order, so the merge's source-index tie-break resolves on
declaration order regardless of the caller's supply order. The narrow C23 amendment
(a `SourceSpec.role` is load-bearing for source binding, the rest of the flat graph
stays raw-index) is deferred to the ledger note.

The four error-path RED tests assert via `.map(|_| ()).unwrap_err()`: the `Ok` arm
`Vec<Box<dyn Source>>` is not `Debug` (`Source` has no `Debug` supertrait), so a bare
`.unwrap_err()` would not compile — a plan-byte defect corrected here.

Also sweeps the 45 raw-index `SourceSpec { .. }` literals to `SourceSpec::raw(..)`
across the workspace (mechanical, compiler-enumerated) and pins that a bound root
role's name survives lowering.

Verification: `cargo test --workspace` green (0 failed; incl. 5 `bind_sources` cases,
the `run_bound` byte-identity test, the role-survives-lowering pin, and the four
`.sources`-equality twins under the now-stricter `role` equality);
`cargo build --workspace --all-targets` clean; `cargo clippy -p aura-engine
--all-targets` clean.

crates/aura-ingest/examples/shared/breakout_real.rs

@@ -184,10 +184,7 @@ pub fn build_harness() -> (Harness, Taps) {
     // declaration order open(0), high(1), low(2), close(3) is the merge tie-break
     // order for the Barrier(0) group — identical to the synthetic capstone.
     let sources = (0..4)
-        .map(|slot| SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![Target { node: RESAMPLE, slot }],
-        })
+        .map(|slot| SourceSpec::raw(ScalarKind::F64, vec![Target { node: RESAMPLE, slot }]))
         .collect();
 
     let h = Harness::bootstrap(FlatGraph { nodes, signatures, sources, edges })

crates/aura-ingest/tests/real_bars.rs

@@ -47,14 +47,11 @@ fn run_sample_over(prices: Vec<(Timestamp, Scalar)>) -> RunReport {
             f64_recorder_sig(),
             f64_recorder_sig(),
         ],
-        sources: vec![SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![
+        sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                 Target { node: 0, slot: 0 },
                 Target { node: 1, slot: 0 },
                 Target { node: 4, slot: 1 }, // price into the broker
-            ],
-        }],
+            ])],
         edges: vec![
             Edge { from: 0, to: 2, slot: 0, from_field: 0 },
             Edge { from: 1, to: 2, slot: 1, from_field: 0 },

crates/aura-ingest/tests/streaming_seam.rs

@@ -53,14 +53,11 @@ fn run_sample(window: (Timestamp, Timestamp), source: Box<dyn Source>) -> RunRep
             f64_recorder_sig(),
             f64_recorder_sig(),
         ],
-        sources: vec![SourceSpec {
-            kind: ScalarKind::F64,
-            targets: vec![
+        sources: vec![SourceSpec::raw(ScalarKind::F64, vec![
                 Target { node: 0, slot: 0 },
                 Target { node: 1, slot: 0 },
                 Target { node: 4, slot: 1 },
-            ],
-        }],
+            ])],
         edges: vec![
             Edge { from: 0, to: 2, slot: 0, from_field: 0 },
             Edge { from: 1, to: 2, slot: 1, from_field: 0 },