docs(r3): add affected-set Introspect-lens prototype canvas

docs/briefs/r3-affected-set-introspect-lens-prototype-worker.md

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+# R3 affected-set Introspect-lens prototype — substrate-composition implementation
+
+**Status:** PRE-AUTHED SUBSTRATE-FEASIBILITY PROBE before implementation. Canvas-driven rebuild for gunbc#2699; supersedes silent-bat-152 PR #2701 once a replacement implementation PR opens. The worker may proceed to implementation only after showing the before/after/dimension inputs can be represented with existing `.dag` substrate and tests-as-data fixtures; otherwise the correct outcome is escalation for substrate-extension authority, not a workaround PR.
+
+**Owner:** worker TBD on dispatch. Coordinator: R3 Verification Mgr (`clever-tern-670`). PM/Director escalation path: deep-wolf-155 / zesty-bear-812.
+
+**Design authority:** [`docs/design-affected-set-lens.md`](../design-affected-set-lens.md), especially §0 locked substrate-vs-adapter terminology, §2 dimension-parameterized affected-set definition, §3 substrate-composition algorithm sketch, and §4 worked examples.
+
+**Context:** PR #2701 is being closed as superseded because it introduced a large hand-Rust affected-set implementation and increased the SG-0 hand surface. This rebuild must prove the same prototype shape through `.dag` substrate composition, not a new Rust analysis engine.
+
+---
+
+## §0. Locked framing
+
+The affected-set surface is an **Introspect lens-family prototype**, not a new query substrate.
+
+- The lens lives at `src/v3/lenses/affected_set_lens.dag`.
+- The substrate output is `Set<NodeRef>` or a `NodeRef`-keyed record carrying dimension and provenance.
+- User-facing CLI / IDE / agent rendering (`{file, span}`, symbols, line ranges) is an adapter boundary after substrate output exists.
+- No `Query` type, no parallel affected-set Rust engine, and no hand-maintained downstream graph.
+
+Live substrate check: `src/v3/std/lens_application.dag` currently exposes `IntrospectApplication<Output>` as `{ lens, section, span }`. It does **not** yet declare `Dag_before` / `Dag_after` / `dim` input fields. The worker composes only what exists. If the before/after/dimension inputs from the design cannot be represented with existing `.dag` facts and fixtures, STOP and escalate instead of inventing a new substrate carrier or filling the gap with Rust.
+
+## §1. Deliverable
+
+Implement the pre-R3-close prototype from `docs/design-affected-set-lens.md` §7:
+
+1. First produce a substrate-feasibility receipt in the implementation PR body naming the actual carriers used for before/after/dimension inputs and output. If the only honest answer is "missing substrate", STOP and escalate before adding `affected_set_lens.dag`.
+2. Add `src/v3/lenses/affected_set_lens.dag` as the substrate authority for the affected-set Introspect lens only after that receipt is grounded.
+3. Keep the lens compact and compositional. Expected size is roughly 20-50 lines unless a clearly cited substrate shape forces slightly more.
+4. Add tests-as-data fixtures only under `src/v3/compiler/tests/dag/`.
+5. Demonstrate three real PR outputs from the gunbc#2699 charter:
+   - PR #2693: v2 directory delete
+   - PR #2679: gate #4 `workflow_idempotency`
+   - PR #2647: quantifier substrate
+6. Each real-PR output must include per-dimension affected-set data plus commentary on why the set is narrower than naive transitive-downstream.
+7. Prove the fixtures execute through an existing zero-SG-0 runner path. `tests/dag/` is not self-discovering on current main; live execution is still mediated by Rust `TestRunner` / suite wiring. The implementation PR must name the existing runner/suite path that executes the new `TestClaim`s, or STOP if execution would require adding a new Rust integration test/table entry.
+
+## §2. Required substrate composition
+
+The implementation must cite and consume these substrate pieces:
+
+| Piece | Authority | Required role |
+| --- | --- | --- |
+| `IntrospectApplication` output carrier | `src/v3/std/lens_application.dag` | User-surface introspect mode; no enforcement budget axis. Consume the existing `{ lens, section, span }` carrier shape only. Output must preserve the design's allowed substrate shape: `Set<NodeRef>` or a `NodeRef`-keyed record carrying dimension/provenance. If before/after/dimension inputs cannot be represented without new substrate, STOP. |
+| `Dag` graph edges | v3 substrate / `Dag` shape | Reverse-edge traversal over the compiled graph. |
+| `DescentEvidence` | `src/v3/std/termination.dag` | Call-site descent lattice; narrows propagation when evidence is known. |
+| `SubValueRelation` | `src/v3/std/induction.dag` | Tracks which sub-piece flows through a call/refinement edge. |
+| `Cardinality` substrate facts | `src/v3/std/substrate.dag` plus existing `src/v3/lenses/*` consumers of `Cardinality` | Distinguishes opaque-carrier changes from structural cardinality/data-shape changes. There is no dedicated `cardinality.dag` lens on `origin/main`; do not require one unless escalated. |
+| `cross_target_coverage` | `src/v3/std/cross_target_coverage.dag` | Narrows target-specific propagation rather than marking every target consumer. |
+| `TestClaim` | `src/v3/std/verification.dag` | Tests are data; affected-set can intersect with TestClaim references. |
+
+If any required substrate piece is missing or cannot be consumed from `.dag`, STOP and escalate. Do not fill the gap with Rust.
+
+## §3. Dimension semantics
+
+The prototype must preserve the dimension-parameterized shape from the design:
+
+- dimensions: `value`, `cost`, `complexity`, `effect`, `refinement`
+- seed nodes with a **PROVEN** delta in that dimension, plus nodes whose dimension delta cannot be proven empty
+- exclude a node only when the lens emits a receipt proving `delta(dim) == empty` for that consumer
+- propagate only through typed edges where that dimension is read by the consumer
+- emit or fixture a per-dimension affected-set output, not just one undifferentiated set
+
+Unknowns must not silently disappear. If the lens cannot prove `delta(dim) == empty`, the affected consumer stays in the affected-set and the fixture commentary must say why.
+
+## §4. Hard constraints
+
+1. **No hand-Rust analysis engine.** Do not add `src/v3/compiler/src/affected_set*.rs` or comparable host-side graph logic.
+2. **Near-zero Rust budget.** A user-surface adapter is legitimate only at a CLI/rendering boundary and only with explicit canvas-tier justification citing the substrate gap that prevents `.dag` rendering. This prototype should not need one.
+3. **Tests-as-data only.** Add `TestClaim` fixtures under `src/v3/compiler/tests/dag/`. Do not add Rust integration tests, unit tests, or SG-0 entries.
+4. **SG-0 delta must be zero or negative.** Positive SG-0 delta is a stop signal. Escalate to PM/Director before pushing.
+5. **No template-only fake.** The lens body must compose substrate facts. A table of hand-authored PR-name-to-output templates does not satisfy the brief.
+6. **No new substrate carriers unless escalated.** The prototype consumes existing carriers and substrate facts named above. New `DagDiff`, `DimensionInput`, query, or specialized cardinality-lens substrate requires canvas-tier approval before implementation.
+7. **No new Rust runner bridge.** The executable receipt must use an existing zero-SG-0 test-as-data runner path. Adding a Rust integration test, fixture registry, or ad hoc table entry just to discover this lens's fixtures is a stop condition, not part of this canvas.
+
+## §5. Acceptance
+
+The implementation PR is acceptable when all are true:
+
+- `src/v3/lenses/affected_set_lens.dag` exists and is the only affected-set lens authority.
+- The PR body includes a substrate-feasibility receipt naming the actual existing carriers/fixtures used for before/after/dimension inputs and output.
+- The lens is modeled against the existing `IntrospectApplication<Output>` carrier without pretending it already has `Dag_before` / `Dag_after` / `dim` fields. If the prototype uses fixture data to represent those design inputs, the PR body must identify that as prototype evidence and name the substrate gap for follow-up.
+- The `.dag` tests-as-data fixtures cover:
+  - dimension-specific outputs for value, cost, complexity, effect, refinement
+  - fail-closed unknown-delta behavior
+  - the three real PRs named in §1
+- The PR body includes a zero-SG-0 executable receipt naming the existing `TestRunner` / suite path that executed those fixtures, with the command and result.
+- Fixture commentary explains narrowing vs naive transitive-downstream for each real PR.
+- SG-0 hand-authored Rust count does not increase.
+- PR body includes: `Supersedes PR #2701` and a closure note that #2701 should close as superseded once the replacement PR is open.
+
+## §6. Stop and escalate
+
+Escalate with `dashboard-message send --to parent --body "..."` if:
+
+- implementing the lens appears to require Rust graph traversal outside an adapter boundary
+- before/after/dimension inputs cannot be represented using existing `.dag` substrate and tests-as-data fixtures
+- a required substrate fact is absent or only available through a host mirror
+- a TestClaim cannot express the prototype output without a new predicate/carrier
+- the new `TestClaim` fixtures cannot execute through an existing zero-SG-0 runner/suite path
+- the SG-0 delta would be positive
+- the worked real-PR outputs cannot be represented as `Set<NodeRef>` / dimension-keyed records
+
+Do not push a workaround PR for any of these; the point of this rebuild is to avoid repeating PR #2701's hand-Rust path.
+
+---
+
+**End of canvas.**