Migrate wire shape to unified fallbacks array

[Copilot]

Replaces the separate falsyFallback/falsyFallbackRefs/falsyControl/nullishFallback/nullishFallbackRefs/nullishControl properties on Wire with a single ordered fallbacks: WireFallback[] array. This enables mixing || and ?? operators in any order within a single wire expression.

o.label <- a.label ?? b.label || c.label ?? "default"

export interface WireFallback {
  type: "falsy" | "nullish";
  ref?: NodeRef;
  value?: string;
  control?: ControlFlowInstruction;
}

Type system (bridge-core)

• Added WireFallback interface, replaced 6 per-variant fallback properties with fallbacks?: WireFallback[]
• resolveWires.ts: Collapsed applyFalsyGate + applyNullishGate into applyFallbackGates — iterates array left-to-right, checking gate type per entry
• tree-utils.ts: Simplified getSimplePullRef fast-path to !w.fallbacks?.length

Parser (bridge-parser)

• New coalesceChainItem grammar rule wrapping || alt and ?? alt into a single OR, replacing the two separate MANY blocks that forced all || before all ??
• All 4 grammar contexts updated (wire, element, scope, alias)
• Visitor produces ordered fallbacks[] preserving authored interleaving
• Serializer reads from fallbacks[], emitting || or ?? based on type

Compiler (bridge-compiler)

• applyFallbacks method iterates w.fallbacks sequentially, emitting || or ?? JS operators per entry

Tests

• 994 tests pass (was 987 — added 7 mixed-chain integration tests)
• Gate unit tests rewritten for applyFallbackGates with 5 new mixed-chain cases
• Round-trip serializer tests for mixed chains
• Parser assertion tests verifying fallbacks array shape

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Change wire shape</issue_title>
<issue_description>Migrate away from falsyFallback and nullishFallback to a unified fallbacks array that will allow mixing ?? and || in any order.

fallback logic will be processed as

      // Layer 1: Execution
      let value = await evaluateWireSource(ctx, w, pullChain);

      // Layer 2: Fallback Gates
      if (w.fallbacks) {
        for (const fallback of w.fallbacks) {
          const isFalsyGateOpen = fallback.type === 'falsy' && !value;
          const isNullishGateOpen = fallback.type === 'nullish' && value == null;

          if (isFalsyGateOpen || isNullishGateOpen) {
            if (fallback.control) return applyControlFlow(fallback.control);
            if (fallback.ref) {
              value = await ctx.pullSingle(fallback.ref, pullChain);
            } else if (fallback.value !== undefined) {
              value = coerceConstant(fallback.value);
            }
          }
        }
      }

new wire types

/**
 * A wire connects a data source (from) to a data sink (to).
 * Execution is pull-based: when "to" is demanded, "from" is resolved.
 *
 * Constant wires (`=`) set a fixed value on the target.
 * Pull wires (`<-`) resolve the source at runtime.
 * Pipe wires (`pipe: true`) are generated by the `<- h1:h2:source` shorthand
 * and route data through declared tool handles; the serializer collapses them
 * back to pipe notation.
 * Spread wires (`spread: true`) merge source object properties into the target.
 */
export interface WireFallback {
  type: "falsy" | "nullish";
  ref?: NodeRef;
  value?: string;
  control?: ControlFlowInstruction;
}

export type Wire =
  | {
      from: NodeRef;
      to: NodeRef;
      pipe?: true;
      /** When true, this wire merges source properties into target (from `...source` syntax). */
      spread?: true;
      safe?: true;
      fallbacks?: WireFallback[];
      catchFallback?: string;
      catchFallbackRef?: NodeRef;
      catchControl?: ControlFlowInstruction;
    }
  | { value: string; to: NodeRef }
  | {
      cond: NodeRef;
      thenRef?: NodeRef;
      thenValue?: string;
      elseRef?: NodeRef;
      elseValue?: string;
      to: NodeRef;
      fallbacks?: WireFallback[];
      catchFallback?: string;
      catchFallbackRef?: NodeRef;
      catchControl?: ControlFlowInstruction;
    }
  | {
      /** Short-circuit logical AND: evaluate left first, only evaluate right if left is truthy */
      condAnd: {
        leftRef: NodeRef;
        rightRef?: NodeRef;
        rightValue?: string;
        safe?: true;
        rightSafe?: true;
      };
      to: NodeRef;
      fallbacks?: WireFallback[];
      catchFallback?: string;
      catchFallbackRef?: NodeRef;
      catchControl?: ControlFlowInstruction;
    }
  | {
      /** Short-circuit logical OR: evaluate left first, only evaluate right if left is falsy */
      condOr: {
        leftRef: NodeRef;
        rightRef?: NodeRef;
        rightValue?: string;
        safe?: true;
        rightSafe?: true;
      };
      to: NodeRef;
      fallbacks?: WireFallback[];
      catchFallback?: string;
      catchFallbackRef?: NodeRef;
      catchControl?: ControlFlowInstruction;
    };

```</issue_description>

<agent_instructions>this is a rather large change :)

- make sure to rely on tests
- write a changeset
- add new tests for cases of mixed wires like A ?? B || C ?? D
- make sure playground has examples for mixed wires
- syntax highlighting in LSP and code-mirror needs updates also

good luck ... i believe in you
gemini 3.1 pro already failed on tis one</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Change wire shape #97

---

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[changeset-bot]

🦋 Changeset detected

Latest commit: f248857

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@stackables/bridge-core	Minor
@stackables/bridge-parser	Minor
@stackables/bridge-compiler	Minor
@stackables/bridge	Minor
@stackables/bridge-graphql	Patch

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Bencher Report

Branch	copilot/change-wire-shape-fallbacks
Testbed	ubuntu-latest

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Benchmark	Latency	nanoseconds (ns)
compiled: absolute baseline (passthrough, no tools)	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
compiled: array + tool-per-element 10	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
compiled: array + tool-per-element 100	📈 view plot ⚠️ NO THRESHOLD	0.03 ns
compiled: chained 3-tool fan-out	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
compiled: flat array 10 items	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
compiled: flat array 100 items	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
compiled: flat array 1000 items	📈 view plot ⚠️ NO THRESHOLD	0.07 ns
compiled: nested array 10x10	📈 view plot ⚠️ NO THRESHOLD	0.02 ns
compiled: nested array 20x10	📈 view plot ⚠️ NO THRESHOLD	0.03 ns
compiled: nested array 5x5	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
compiled: short-circuit (overdefinition bypass)	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
compiled: simple chain (1 tool)	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
exec: absolute baseline (passthrough, no tools)	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
exec: array + tool-per-element 10	📈 view plot ⚠️ NO THRESHOLD	0.08 ns
exec: array + tool-per-element 100	📈 view plot ⚠️ NO THRESHOLD	0.68 ns
exec: chained 3-tool fan-out	📈 view plot ⚠️ NO THRESHOLD	0.02 ns
exec: flat array 10 items	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
exec: flat array 100 items	📈 view plot ⚠️ NO THRESHOLD	0.07 ns
exec: flat array 1000 items	📈 view plot ⚠️ NO THRESHOLD	0.66 ns
exec: nested array 10x10	📈 view plot ⚠️ NO THRESHOLD	0.12 ns
exec: nested array 20x10	📈 view plot ⚠️ NO THRESHOLD	0.24 ns
exec: nested array 5x5	📈 view plot ⚠️ NO THRESHOLD	0.05 ns
exec: short-circuit (overdefinition bypass)	📈 view plot ⚠️ NO THRESHOLD	0.00 ns
exec: simple chain (1 tool)	📈 view plot ⚠️ NO THRESHOLD	0.01 ns
parse: large bridge (20 handles x 5 wires)	📈 view plot ⚠️ NO THRESHOLD	1.10 ns
parse: simple bridge	📈 view plot ⚠️ NO THRESHOLD	0.04 ns

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