diff --git a/.changeset/1959-sbfl-fault-localization.md b/.changeset/1959-sbfl-fault-localization.md
new file mode 100644
index 000000000..e01ce733c
--- /dev/null
+++ b/.changeset/1959-sbfl-fault-localization.md
@@ -0,0 +1,5 @@
+---
+type: Added
+pr: 2403
+---
+**`gsd-debugger` now ranks suspect code by Ochiai suspiciousness before forming hypotheses** — when a runnable test suite with per-test coverage exists (≥1 failing and ≥1 passing test), the debugger computes a spectrum-based fault-localization (Ochiai) ranking over the coverage and seeds the top-N suspicious locations into the Evidence section as first-class hypothesis candidates, narrowing the search space deterministically before any LLM reasoning. Tarantula is documented as a fallback formula. The step degrades cleanly (logged, never a silent pass) when there is no test suite, no failing tests, or no per-test coverage, and it is explicitly not trusted on flaky/Heisenbug spectra (pairs with the Phase 2B bug-taxonomy routing). Full rules live in `gsd-core/references/debugger-sbfl.md`. (#1959)
diff --git a/agents/gsd-debugger.md b/agents/gsd-debugger.md
index d4a8884ec..cbd11ac11 100644
--- a/agents/gsd-debugger.md
+++ b/agents/gsd-debugger.md
@@ -983,6 +983,13 @@ At investigation decision points, apply structured reasoning:
 - Run app/tests to observe behavior
 - APPEND to Evidence after each finding
 
+**Phase 1.25: Spectrum-based fault localization (optional, coverage-gated)**
+- When a runnable test suite with per-test coverage exists (≥1 failing AND ≥1 passing test), compute an Ochiai suspiciousness ranking and seed the top-N into Evidence before forming hypotheses — narrows the search space deterministically before LLM reasoning:
+
+@~/.claude/gsd-core/references/debugger-sbfl.md
+
+- Skip with a logged note when there is no test suite, no failing tests, or no per-test coverage; investigation proceeds unchanged
+
 **Phase 1.5: Check common bug patterns**
 - Read @~/.claude/gsd-core/references/common-bug-patterns.md
 - Match symptoms to pattern categories using the Symptom-to-Category Quick Map
diff --git a/docs/AGENTS.md b/docs/AGENTS.md
index 5b4d268f4..8751711c1 100644
--- a/docs/AGENTS.md
+++ b/docs/AGENTS.md
@@ -401,6 +401,7 @@ runs its default whole-repo scan.
 - State persists across context resets
 - Requires human verification before marking resolved
 - Runs a multi-signal fix-acceptance guardrail (mutation check, no-op/deletion detector, adjacent tests, revert-and-reconfirm) before accepting a fix; degrades gracefully when Stryker or a test suite is absent
+- Ranks suspect code by Ochiai suspiciousness from test pass/fail coverage (spectrum-based fault localization) before forming hypotheses; skips cleanly when no coverage exists
 - Appends to persistent knowledge base on resolution
 - Consults knowledge base on new sessions
 
diff --git a/docs/INVENTORY-MANIFEST.json b/docs/INVENTORY-MANIFEST.json
index d0123c9f9..54e8df122 100644
--- a/docs/INVENTORY-MANIFEST.json
+++ b/docs/INVENTORY-MANIFEST.json
@@ -216,6 +216,7 @@
       "continuation-format.md",
       "debugger-fix-acceptance.md",
       "debugger-philosophy.md",
+      "debugger-sbfl.md",
       "decimal-phase-calculation.md",
       "doc-conflict-engine.md",
       "domain-probes.md",
diff --git a/docs/INVENTORY.md b/docs/INVENTORY.md
index 30ee818b7..0d6da296a 100644
--- a/docs/INVENTORY.md
+++ b/docs/INVENTORY.md
@@ -295,6 +295,7 @@ Full roster at `gsd-core/references/*.md`. References are shared knowledge docum
 | `common-bug-patterns.md` | Common bug patterns for code review and verification. |
 | `debugger-philosophy.md` | Evergreen debugging disciplines loaded by `gsd-debugger`. |
 | `debugger-fix-acceptance.md` | Multi-signal fix-acceptance guardrail (anti-overfitting) loaded by `gsd-debugger`. |
+| `debugger-sbfl.md` | Spectrum-based fault localization (Ochiai) pre-filter loaded by `gsd-debugger`. |
 | `mandatory-initial-read.md` | Shared required-reading boilerplate injected into agent prompts. |
 | `agent-skills-bootstrap.md` | Shared agent_skills self-load contract (query + Read + dedup guard) injected into all 22 consumer agents. |
 | `project-skills-discovery.md` | Shared project-skills-discovery boilerplate injected into agent prompts. |
diff --git a/gsd-core/references/debugger-sbfl.md b/gsd-core/references/debugger-sbfl.md
new file mode 100644
index 000000000..ddd542f9d
--- /dev/null
+++ b/gsd-core/references/debugger-sbfl.md
@@ -0,0 +1,110 @@
+# Spectrum-Based Fault Localization (SBFL) Pre-filter
+
+Loaded by `gsd-debugger` via `@-include`. A deterministic ranked "where to look
+first" list derived from existing test pass/fail coverage, computed before LLM
+reasoning over an unranked search space.
+
+## Why this exists
+
+`investigation_loop` Phase 1 searches the codebase and reads files to seed
+hypotheses via (expensive, non-deterministic) LLM reasoning over an unranked
+space. When a runnable test suite with per-test coverage exists, there is a
+cheap, deterministic signal being left on the table: which code is
+disproportionately executed by **failing** vs **passing** tests. SBFL turns
+that coverage spectrum into a suspiciousness ranking. The agent currently has no
+fault-localization step at all.
+
+## When to run it (Phase 1.25 — after initial evidence, before hypothesis formation)
+
+Run only when ALL hold:
+- A runnable test suite exists for the failing area.
+- At least one failing test AND at least one passing test exist (a spectrum
+  requires both).
+- Per-test coverage is available (which tests executed which code
+  element — function, line, or branch).
+
+If any precondition fails, **skip** this step with a logged note (see
+Degradation) and proceed with Phase 1's normal evidence gathering unchanged.
+
+## The Ochiai formula
+
+For each code element `s` executed by the test suite:
+
+```
+ochiai(s) = failed(s) / sqrt(totalFailed × (failed(s) + passed(s)))
+```
+
+where:
+- `failed(s)` = number of **failing** tests that executed `s`
+- `passed(s)` = number of **passing** tests that executed `s`
+- `totalFailed` = total number of failing tests in the suite
+
+The score is in `[0, 1]`. An element executed by every failing test and no
+passing test scores `1.0` (maximum suspiciousness). An element touched only by
+passing tests scores `0`. Ochiai is empirically stronger than Tarantula across
+the SBFL literature; **Tarantula** is the documented fallback formula
+(`tarantula(s) = (failed(s)/totalFailed) / ((failed(s)/totalFailed) + (passed(s)/totalPassed))`)
+if a comparison or secondary signal is wanted.
+
+## Output — top-N shortlist seeded into the hypothesis space
+
+Rank all executed elements by descending Ochiai score and take the **top-N**
+(N is judgment — 5–10 is typical; bounded by what narrows the search without
+flooding it). Append each top-N element to the debug file's **Evidence**
+section as a first-class hypothesis candidate:
+
+```
+- timestamp: <now>
+  checked: SBFL Ochiai ranking (Phase 1.25)
+  found: top-N suspicious locations —
+    1. path/to/file.cts:LINE (score 0.89) — <symbol>
+    2. path/to/other.cts:LINE (score 0.77) — <symbol>
+    ...
+  implication: investigate these before forming broader hypotheses
+```
+
+This narrows the search space by orders of magnitude before any LLM tokens are
+spent forming hypotheses. Each top-N entry becomes a candidate for Phase 2
+hypothesis formation, ranked ahead of un-evidenced guesses.
+
+## Degradation (Gall's Law — optional step, degrades onto the working agent)
+
+This step is **purely additive**. Every miss degrades to today's behavior; a
+skipped step is logged, never a silent pass (Kernighan — the debugger stays
+auditable).
+
+| Condition | Behavior |
+|---|---|
+| No test suite for the failing area | **skip** with a logged note in Evidence ("SBFL skipped: no test suite"); Phase 1 proceeds unchanged |
+| Test suite but no failing tests | **skip** with a logged note ("SBFL skipped: no failing tests — no spectrum"); Phase 1 proceeds unchanged |
+| Test suite but no passing tests | **skip** with a logged note ("SBFL skipped: no spectrum — no passing tests"); Phase 1 proceeds unchanged (Tarantula would divide by `totalPassed=0`; do not run it) |
+| Test suite but no per-test coverage | **skip** with a logged note ("SBFL skipped: no per-test coverage available"); Phase 1 proceeds unchanged |
+| Coverage exists but is coarse (file-level, not line/function) | run anyway, rank at the available granularity, and note the granularity in Evidence |
+
+## Bug-class gating (pairs with Phase 2B bug-taxonomy routing)
+
+SBFL is the go-to pre-filter for **deterministic failures (Bohrbugs)** — bugs
+that reproduce reliably. It is explicitly **not trusted** on
+**Heisenbug/Mandelbug** spectra (timing, races, environment-dependent failures):
+a flaky suite pollutes the spectrum (a "failing" test that sometimes passes
+poisons `failed(s)`), so the ranking becomes noise. When the failure is
+non-deterministic (Phase 2B classifies it), **skip SBFL** and route to
+record-replay or stability-stress instead. If SBFL has already run before
+classification and the class later resolves to Heisenbug/Mandelbug, mark the
+prior SBFL Evidence entry as revoked (do not delete it — Kernighan
+auditability) and note why in Evidence.
+
+## Scope boundary (Zawinski's Law)
+
+This is a deterministic pre-filter that reuses the project's existing
+test/coverage runner — it adds **no new coverage framework** and no new
+subsystem. It narrows the LLM's search space; it does not replace hypothesis
+formation, fix-and-verify, or the knowledge base. Coverage acquisition is the
+agent's adaptive job (use whatever coverage the project produces); the formula
+above is the canonical ranking.
+
+**Bound the coverage run** (CLAUDE.md gauntlet — unbounded subprocess): a
+coverage run is often 2–3× slower than a plain test run due to instrumentation,
+so cap it (60s for npm-tier suites; scale with suite size) and **degrade to
+skip with a logged note on timeout** — never let coverage acquisition hang the
+debug session.
diff --git a/tests/agent-size-baseline.json b/tests/agent-size-baseline.json
index f532f9a11..2d0c7ffe1 100644
--- a/tests/agent-size-baseline.json
+++ b/tests/agent-size-baseline.json
@@ -6,7 +6,7 @@
   "gsd-code-reviewer.md": 16870,
   "gsd-codebase-mapper.md": 21485,
   "gsd-debug-session-manager.md": 16850,
-  "gsd-debugger.md": 52209,
+  "gsd-debugger.md": 52734,
   "gsd-doc-classifier.md": 11717,
   "gsd-doc-synthesizer.md": 13154,
   "gsd-doc-verifier.md": 12403,
diff --git a/tests/debugger-sbfl.test.cjs b/tests/debugger-sbfl.test.cjs
new file mode 100644
index 000000000..a22c5cb77
--- /dev/null
+++ b/tests/debugger-sbfl.test.cjs
@@ -0,0 +1,198 @@
+// allow-test-rule: source-text-is-the-product (see #1959)
+// Agent .md + reference .md files — their text IS what the runtime loads.
+// Testing text content tests the deployed SBFL contract. The pure-JS Ochiai
+// tests below validate the formula the reference documents (criterion 2:
+// known-faulty location in top-N). Per CONTRIBUTING.md exception matrix.
+// Covers epic #1957 Phase 1B (#1959).
+'use strict';
+
+const { describe, test } = require('node:test');
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+let fc;
+try {
+  fc = require('fast-check');
+} catch {
+  fc = null;
+}
+
+const ROOT = process.cwd();
+const AGENT = path.join(ROOT, 'agents/gsd-debugger.md');
+const REFERENCE = path.join(ROOT, 'gsd-core/references/debugger-sbfl.md');
+
+// In-test canonical Ochiai implementation — validates the formula the reference
+// documents. If the reference's formula drifts from real Ochiai, the contract
+// tests (Ochiai named + formula shape) flag the drift, and these correctness
+// tests pin what "correct Ochiai" means.
+function ochiai(failedExec, passedExec, totalFailed) {
+  if (totalFailed <= 0) return 0;
+  const denom = Math.sqrt(totalFailed * (failedExec + passedExec));
+  return denom === 0 ? 0 : failedExec / denom;
+}
+
+function rankByOchiai(elements, totalFailed) {
+  return elements
+    .map((e) => ({ element: e.element, score: ochiai(e.failedExec, e.passedExec, totalFailed) }))
+    .sort((a, b) => b.score - a.score);
+}
+
+describe('spectrum-based fault localization (#1959, epic #1957 Phase 1B)', () => {
+  describe('reference extract exists and is wired into the agent', () => {
+    test('gsd-core/references/debugger-sbfl.md exists', () => {
+      assert.ok(fs.existsSync(REFERENCE), 'debugger-sbfl.md reference must exist');
+    });
+
+    test('gsd-debugger.md @-includes the SBFL reference', () => {
+      const content = fs.readFileSync(AGENT, 'utf8');
+      assert.ok(
+        content.includes('@~/.claude/gsd-core/references/debugger-sbfl.md'),
+        'gsd-debugger.md must @-include the SBFL reference'
+      );
+    });
+  });
+
+  describe('Ochiai contract documented (criterion 1)', () => {
+    test('reference names Ochiai and documents the formula', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/ochiai/i.test(content), 'reference must name the Ochiai formula');
+      assert.ok(/sqrt/i.test(content), 'reference must document the sqrt-based formula');
+      assert.ok(/failed/i.test(content) && /passed/i.test(content),
+        'reference must reference failed(s) and passed(s) terms');
+    });
+
+    test('reference documents Tarantula as a fallback', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/tarantula/i.test(content), 'reference must mention Tarantula as a documented fallback');
+    });
+
+    test('reference documents top-N seeding into the hypothesis space', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/top-?n/i.test(content), 'reference must document top-N shortlist seeding');
+    });
+  });
+
+  describe('graceful degradation (criterion 3)', () => {
+    test('reference documents skip when no coverage / no test suite', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/no coverage|no test suite|coverage (?:is )?(?:absent|unavailable)/i.test(content),
+        'must document the no-coverage skip path');
+      assert.ok(/skip.*log|log.*skip|skip.*note|note.*skip/i.test(content),
+        'skip must be logged (not a silent pass) — Kernighan auditability');
+    });
+  });
+
+  describe('ranking written to the debug file as seed evidence (criterion 4)', () => {
+    test('reference documents recording the ranking under Evidence', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/evidence/i.test(content),
+        'reference must document that the ranking lands in the Evidence section of the debug file');
+    });
+  });
+
+  describe('pairs with Phase 2B bug-taxonomy routing', () => {
+    test('reference notes SBFL is gated for deterministic (Bohrbug) failures', () => {
+      const content = fs.readFileSync(REFERENCE, 'utf8');
+      assert.ok(/bohrbug|deterministic|flaky|heisenbug|mandelbug/i.test(content),
+        'reference must note SBFL suits deterministic bugs and is not trusted on flaky spectra (pairs with Phase 2B)');
+    });
+  });
+
+  describe('Ochiai formula correctness — behavioral (criterion 2: known-faulty location in top-N)', () => {
+    test('score is always in [0, 1] for any non-negative inputs (totalFailed > 0)', () => {
+      const fixture = [
+        { failedExec: 0, passedExec: 10, totalFailed: 5 },
+        { failedExec: 5, passedExec: 0, totalFailed: 5 },
+        { failedExec: 3, passedExec: 7, totalFailed: 5 },
+        { failedExec: 5, passedExec: 100, totalFailed: 5 },
+      ];
+      for (const f of fixture) {
+        const s = ochiai(f.failedExec, f.passedExec, f.totalFailed);
+        assert.ok(s >= 0 && s <= 1, `score ${s} out of [0,1] for failedExec=${f.failedExec} passedExec=${f.passedExec} totalFailed=${f.totalFailed}`);
+      }
+    });
+
+    test('an element hit by all failing tests and no passing tests scores the maximum (1.0)', () => {
+      assert.strictEqual(ochiai(5, 0, 5), 1);
+      assert.strictEqual(ochiai(1, 0, 1), 1);
+    });
+
+    test('a known-faulty element ranks in the top-N of a representative fixture', () => {
+      // Representative fixture: 5 tests (3 failing, 2 passing), 4 code elements.
+      // Element "bug" is executed by all 3 failing tests and 0 passing → Ochiai 1.0 → rank #1.
+      const totalFailed = 3;
+      const elements = [
+        { element: 'unrelated-a', failedExec: 1, passedExec: 2 },
+        { element: 'bug', failedExec: 3, passedExec: 0 }, // the known fault
+        { element: 'unrelated-b', failedExec: 2, passedExec: 2 },
+        { element: 'unrelated-c', failedExec: 0, passedExec: 2 },
+      ];
+      const ranked = rankByOchiai(elements, totalFailed);
+      const topN = ranked.slice(0, Math.min(3, ranked.length));
+      assert.ok(topN.length > 0, 'ranking must be non-empty');
+      assert.strictEqual(ranked[0].element, 'bug', 'the known-faulty element must rank #1');
+      assert.ok(topN.some((r) => r.element === 'bug'),
+        'the known-faulty element must appear in the top-N (criterion 2)');
+      // ranking is non-increasing
+      for (let i = 1; i < ranked.length; i++) {
+        assert.ok(ranked[i - 1].score >= ranked[i].score, 'ranking must be non-increasing');
+      }
+    });
+
+    test('degrades cleanly when there are no failing tests (totalFailed = 0 → all scores 0)', () => {
+      const elements = [
+        { element: 'a', failedExec: 0, passedExec: 5 },
+        { element: 'b', failedExec: 0, passedExec: 3 },
+      ];
+      const ranked = rankByOchiai(elements, 0);
+      for (const r of ranked) {
+        assert.strictEqual(r.score, 0, 'no failing tests → every suspiciousness score is 0 (clean degradation)');
+      }
+    });
+
+    if (fc) {
+      test('property: ochiai ∈ [0, 1] for valid coverage counts (failedExec ≤ totalFailed)', () => {
+        // Ochiai is defined over coverage counts where failedExec is bounded by
+        // totalFailed (a failing test that executed s is one of the totalFailed
+        // failing tests) and passedExec is bounded by totalPassed. Generate
+        // in-domain inputs via chain.
+        const validCoverage = fc.integer({ min: 1, max: 30 }).chain((totalFailed) =>
+          fc.record({
+            totalFailed: fc.constant(totalFailed),
+            failedExec: fc.integer({ min: 0, max: totalFailed }),
+            passedExec: fc.nat(30),
+          })
+        );
+        fc.assert(
+          fc.property(validCoverage, ({ totalFailed, failedExec, passedExec }) => {
+            const s = ochiai(failedExec, passedExec, totalFailed);
+            return s >= 0 && s <= 1 + 1e-9;
+          }),
+          { numRuns: 200 }
+        );
+      });
+
+      test('property: ochiai is non-decreasing in failedExec (holding totalFailed + passedExec fixed)', () => {
+        // Non-trivial: a correct Ochiai must not penalize an element for being
+        // hit by MORE failing tests. An inverted numerator/denominator would fail this.
+        // failedExecA is bounded by totalFailed (coverage invariant) via chain.
+        const validStart = fc.integer({ min: 1, max: 30 }).chain((totalFailed) =>
+          fc.record({
+            totalFailed: fc.constant(totalFailed),
+            passedExec: fc.nat(30),
+            failedExecA: fc.integer({ min: 0, max: totalFailed }),
+          })
+        );
+        fc.assert(
+          fc.property(validStart, ({ totalFailed, passedExec, failedExecA }) => {
+            const failedExecB = Math.min(totalFailed, failedExecA + 1);
+            if (failedExecB === failedExecA) return true; // A already at totalFailed
+            return ochiai(failedExecB, passedExec, totalFailed) >= ochiai(failedExecA, passedExec, totalFailed) - 1e-9;
+          }),
+          { numRuns: 300 }
+        );
+      });
+    }
+  });
+});
diff --git a/tests/fixtures/golden-install-parity/antigravity.json b/tests/fixtures/golden-install-parity/antigravity.json
index 9f009f92d..fc6d54c8a 100644
--- a/tests/fixtures/golden-install-parity/antigravity.json
+++ b/tests/fixtures/golden-install-parity/antigravity.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "a700d295bbf110a9",
   "agents/gsd-codebase-mapper.md": "afdae82284cb21b4",
   "agents/gsd-debug-session-manager.md": "95441545abeab3f5",
-  "agents/gsd-debugger.md": "c4420686f490d948",
+  "agents/gsd-debugger.md": "a41ea4bc59ea744f",
   "agents/gsd-doc-classifier.md": "fca19595590391df",
   "agents/gsd-doc-synthesizer.md": "0e5184bbcf0dca02",
   "agents/gsd-doc-verifier.md": "888c6ac870cb91a6",
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "87d367e4e864910e",
   "gsd-core/references/debugger-philosophy.md": "1cb61d4565081c88",
+  "gsd-core/references/debugger-sbfl.md": "de9cd1bd0e1485c6",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/augment.json b/tests/fixtures/golden-install-parity/augment.json
index a48446310..acf08f35c 100644
--- a/tests/fixtures/golden-install-parity/augment.json
+++ b/tests/fixtures/golden-install-parity/augment.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "bc8a6f2e1f787ff5",
   "agents/gsd-codebase-mapper.md": "85ea778ad9cf7e66",
   "agents/gsd-debug-session-manager.md": "2f775ae4ab8855a0",
-  "agents/gsd-debugger.md": "a21c4e8d29b0eaee",
+  "agents/gsd-debugger.md": "a0ec84b507f2e036",
   "agents/gsd-doc-classifier.md": "262a94b947a4e2aa",
   "agents/gsd-doc-synthesizer.md": "01f90ea9b0d05d7d",
   "agents/gsd-doc-verifier.md": "b3433e0db51e1c60",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/golden-install-parity/claude-local.json b/tests/fixtures/golden-install-parity/claude-local.json
index 68536223f..060db57c6 100644
--- a/tests/fixtures/golden-install-parity/claude-local.json
+++ b/tests/fixtures/golden-install-parity/claude-local.json
@@ -7,7 +7,7 @@
   "agents/gsd-code-reviewer.md": "e2c45baa8c0b5f6d",
   "agents/gsd-codebase-mapper.md": "f96958e5f85b93fb",
   "agents/gsd-debug-session-manager.md": "7e08652ad1c48efb",
-  "agents/gsd-debugger.md": "a3643fb51b054988",
+  "agents/gsd-debugger.md": "3c0526872ae337d7",
   "agents/gsd-doc-classifier.md": "a76778bdde1c7f72",
   "agents/gsd-doc-synthesizer.md": "8b0b6fc187c9d353",
   "agents/gsd-doc-verifier.md": "4232dcf9076e3566",
@@ -132,6 +132,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/claude.json b/tests/fixtures/golden-install-parity/claude.json
index 29a38707e..f460f1f48 100644
--- a/tests/fixtures/golden-install-parity/claude.json
+++ b/tests/fixtures/golden-install-parity/claude.json
@@ -7,7 +7,7 @@
   "agents/gsd-code-reviewer.md": "d626a828e8de3648",
   "agents/gsd-codebase-mapper.md": "8c2e9f2ce3aedf78",
   "agents/gsd-debug-session-manager.md": "a813e6b226b2be58",
-  "agents/gsd-debugger.md": "dd4baf1337cebe09",
+  "agents/gsd-debugger.md": "fc975cf160dfee7a",
   "agents/gsd-doc-classifier.md": "a636ae9594b25770",
   "agents/gsd-doc-synthesizer.md": "dfb95eedfb3789bf",
   "agents/gsd-doc-verifier.md": "4232dcf9076e3566",
@@ -61,6 +61,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/cline.json b/tests/fixtures/golden-install-parity/cline.json
index 5b66305c2..c38f677e0 100644
--- a/tests/fixtures/golden-install-parity/cline.json
+++ b/tests/fixtures/golden-install-parity/cline.json
@@ -11,7 +11,7 @@
   "agents/gsd-code-reviewer.md": "e5ec12d4d409e800",
   "agents/gsd-codebase-mapper.md": "e5b7941bdda53c91",
   "agents/gsd-debug-session-manager.md": "dd70329c06ec5b79",
-  "agents/gsd-debugger.md": "8709cc2721688ea9",
+  "agents/gsd-debugger.md": "706cc2c87a8da251",
   "agents/gsd-doc-classifier.md": "5011d7358d2b2848",
   "agents/gsd-doc-synthesizer.md": "e59cdd669876582d",
   "agents/gsd-doc-verifier.md": "b60290c9d9f6d8d2",
@@ -65,6 +65,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "1057d70f7f2d654a",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "6e4975ee50973c23",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/golden-install-parity/codebuddy.json b/tests/fixtures/golden-install-parity/codebuddy.json
index d0b80a49e..a7d023273 100644
--- a/tests/fixtures/golden-install-parity/codebuddy.json
+++ b/tests/fixtures/golden-install-parity/codebuddy.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "5342fcc0da974696",
   "agents/gsd-codebase-mapper.md": "b995bf01af0193d2",
   "agents/gsd-debug-session-manager.md": "6dc05c3ac8a3f2cc",
-  "agents/gsd-debugger.md": "5549e84b9b576d9b",
+  "agents/gsd-debugger.md": "54ab502a6b751680",
   "agents/gsd-doc-classifier.md": "c2bf59af9467810b",
   "agents/gsd-doc-synthesizer.md": "b2a179bf3c9bd636",
   "agents/gsd-doc-verifier.md": "e74d930905a782ea",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/golden-install-parity/codex.json b/tests/fixtures/golden-install-parity/codex.json
index cd77bb4bf..7910f70c2 100644
--- a/tests/fixtures/golden-install-parity/codex.json
+++ b/tests/fixtures/golden-install-parity/codex.json
@@ -86,8 +86,8 @@
   "agents/gsd-codebase-mapper.toml": "a4609f3ac66c2081",
   "agents/gsd-debug-session-manager.md": "5c7af4adccaa9597",
   "agents/gsd-debug-session-manager.toml": "e3b962d5478f2b46",
-  "agents/gsd-debugger.md": "aec67e757771e460",
-  "agents/gsd-debugger.toml": "99a17d121197cfa5",
+  "agents/gsd-debugger.md": "fefd9d1a59661bff",
+  "agents/gsd-debugger.toml": "83dbb27716668d91",
   "agents/gsd-doc-classifier.md": "2745bc04d7b93666",
   "agents/gsd-doc-classifier.toml": "3fe5ec83f62b586e",
   "agents/gsd-doc-synthesizer.md": "4f545f2e916458ad",
@@ -168,6 +168,7 @@
   "gsd-core/references/continuation-format.md": "e64c0da2b3d0f2f0",
   "gsd-core/references/debugger-fix-acceptance.md": "b2732420bdbcadcd",
   "gsd-core/references/debugger-philosophy.md": "1cb61d4565081c88",
+  "gsd-core/references/debugger-sbfl.md": "391e732abf32786a",
   "gsd-core/references/decimal-phase-calculation.md": "ee363ec47be68922",
   "gsd-core/references/doc-conflict-engine.md": "257aba80c93854d4",
   "gsd-core/references/domain-probes.md": "4901deac8eac0f49",
diff --git a/tests/fixtures/golden-install-parity/copilot.json b/tests/fixtures/golden-install-parity/copilot.json
index 93063cfee..99f5266d2 100644
--- a/tests/fixtures/golden-install-parity/copilot.json
+++ b/tests/fixtures/golden-install-parity/copilot.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.agent.md": "fa1e7c421c78eae1",
   "agents/gsd-codebase-mapper.agent.md": "949bc73f2a7ea44d",
   "agents/gsd-debug-session-manager.agent.md": "bbea35c986c88ce6",
-  "agents/gsd-debugger.agent.md": "92ba32ed5042d76d",
+  "agents/gsd-debugger.agent.md": "358b4c70a38b4341",
   "agents/gsd-doc-classifier.agent.md": "aea81c0ba00e06cf",
   "agents/gsd-doc-synthesizer.agent.md": "6ae32e4db005696d",
   "agents/gsd-doc-verifier.agent.md": "0230208ae7ab1a08",
@@ -63,6 +63,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "812922e2b5db9410",
   "gsd-core/references/debugger-philosophy.md": "1cb61d4565081c88",
+  "gsd-core/references/debugger-sbfl.md": "5bb65a8653bf2e06",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/cursor.json b/tests/fixtures/golden-install-parity/cursor.json
index 672977db8..1d11089fe 100644
--- a/tests/fixtures/golden-install-parity/cursor.json
+++ b/tests/fixtures/golden-install-parity/cursor.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "f29d6edbac0a01b6",
   "agents/gsd-codebase-mapper.md": "d49c91fdab4efc70",
   "agents/gsd-debug-session-manager.md": "69a051432e54f9a5",
-  "agents/gsd-debugger.md": "3fb544d8fce11aea",
+  "agents/gsd-debugger.md": "ac61fdd3129770c5",
   "agents/gsd-doc-classifier.md": "a6ab02b8f45f9d0b",
   "agents/gsd-doc-synthesizer.md": "fd3c18addbc8265d",
   "agents/gsd-doc-verifier.md": "9934ec11845d41c3",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "86b7cbde0171fafd",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "838445590aab52e3",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/hermes.json b/tests/fixtures/golden-install-parity/hermes.json
index 733fee395..e83e24ea2 100644
--- a/tests/fixtures/golden-install-parity/hermes.json
+++ b/tests/fixtures/golden-install-parity/hermes.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "5ef947ca5baed775",
   "agents/gsd-codebase-mapper.md": "feccaeeacd05e34b",
   "agents/gsd-debug-session-manager.md": "60945a8dcfb7e3d7",
-  "agents/gsd-debugger.md": "0489cee92e1361a7",
+  "agents/gsd-debugger.md": "8a375259b81d8adf",
   "agents/gsd-doc-classifier.md": "29b563a146c9d22c",
   "agents/gsd-doc-synthesizer.md": "652beb928e93fa1d",
   "agents/gsd-doc-verifier.md": "d3d8457bdd44bf10",
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "b04b913d5ea0ac90",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "70e699200f6197e0",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/kilo.json b/tests/fixtures/golden-install-parity/kilo.json
index a03c1af36..55a43199a 100644
--- a/tests/fixtures/golden-install-parity/kilo.json
+++ b/tests/fixtures/golden-install-parity/kilo.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "922c08885bc78662",
   "agents/gsd-codebase-mapper.md": "0ccbf6a685804979",
   "agents/gsd-debug-session-manager.md": "621c4c28af4f7b01",
-  "agents/gsd-debugger.md": "75c345b1ae4a86d2",
+  "agents/gsd-debugger.md": "c9fcb57e5f6e6ee7",
   "agents/gsd-doc-classifier.md": "6256bbc0b887f60f",
   "agents/gsd-doc-synthesizer.md": "212aaf89a34b51d7",
   "agents/gsd-doc-verifier.md": "8016f792d0766b77",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "b2732420bdbcadcd",
   "gsd-core/references/debugger-philosophy.md": "1cb61d4565081c88",
+  "gsd-core/references/debugger-sbfl.md": "391e732abf32786a",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/kimi.json b/tests/fixtures/golden-install-parity/kimi.json
index a5e446a8a..6ddc71261 100644
--- a/tests/fixtures/golden-install-parity/kimi.json
+++ b/tests/fixtures/golden-install-parity/kimi.json
@@ -45,7 +45,7 @@
   "agents/subagents/gsd-codebase-mapper.yaml": "bce1c6d15f55c477",
   "agents/subagents/gsd-debug-session-manager.md": "69b3083e7e29c435",
   "agents/subagents/gsd-debug-session-manager.yaml": "aab147717b5082e7",
-  "agents/subagents/gsd-debugger.md": "3e9607a7ba92cec5",
+  "agents/subagents/gsd-debugger.md": "a2f38433646baffc",
   "agents/subagents/gsd-debugger.yaml": "6d02d7feb90cad43",
   "agents/subagents/gsd-doc-classifier.md": "632dc6c61bafa63e",
   "agents/subagents/gsd-doc-classifier.yaml": "a4e9cf7025b57503",
@@ -126,6 +126,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/golden-install-parity/opencode.json b/tests/fixtures/golden-install-parity/opencode.json
index b24ca55ac..9a6fb216b 100644
--- a/tests/fixtures/golden-install-parity/opencode.json
+++ b/tests/fixtures/golden-install-parity/opencode.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "2249774416314c57",
   "agents/gsd-codebase-mapper.md": "948612acd505e87f",
   "agents/gsd-debug-session-manager.md": "cb64aa404849be60",
-  "agents/gsd-debugger.md": "60df2107066b0006",
+  "agents/gsd-debugger.md": "1653f7447e3fa8a8",
   "agents/gsd-doc-classifier.md": "fb776cfbb7e991b0",
   "agents/gsd-doc-synthesizer.md": "2389f388d291c2eb",
   "agents/gsd-doc-verifier.md": "65bbc2ae6b9ace29",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "b2732420bdbcadcd",
   "gsd-core/references/debugger-philosophy.md": "1cb61d4565081c88",
+  "gsd-core/references/debugger-sbfl.md": "391e732abf32786a",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/pi.json b/tests/fixtures/golden-install-parity/pi.json
index 4ac403d0d..867f181a3 100644
--- a/tests/fixtures/golden-install-parity/pi.json
+++ b/tests/fixtures/golden-install-parity/pi.json
@@ -29,6 +29,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/golden-install-parity/qwen.json b/tests/fixtures/golden-install-parity/qwen.json
index 12892cb7c..0988c71cf 100644
--- a/tests/fixtures/golden-install-parity/qwen.json
+++ b/tests/fixtures/golden-install-parity/qwen.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "27eeeee6cb600e9b",
   "agents/gsd-codebase-mapper.md": "032ff8ac55466a74",
   "agents/gsd-debug-session-manager.md": "e4db798b5a536a2c",
-  "agents/gsd-debugger.md": "8448c971f713412f",
+  "agents/gsd-debugger.md": "a93dd835d97836c7",
   "agents/gsd-doc-classifier.md": "bdf3d54082424e76",
   "agents/gsd-doc-synthesizer.md": "96c383b74a60fbbe",
   "agents/gsd-doc-verifier.md": "da9ab6f3ec27778a",
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "ab6a1cce253944f4",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "061b719c754a12d3",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/trae.json b/tests/fixtures/golden-install-parity/trae.json
index bbbecfd7e..16b8eb1b3 100644
--- a/tests/fixtures/golden-install-parity/trae.json
+++ b/tests/fixtures/golden-install-parity/trae.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "338c46ab59c4e45f",
   "agents/gsd-codebase-mapper.md": "8529d8a1ede8bbfb",
   "agents/gsd-debug-session-manager.md": "5e64d23321942c1c",
-  "agents/gsd-debugger.md": "d7fc667ae590dd6f",
+  "agents/gsd-debugger.md": "1839444836892ffe",
   "agents/gsd-doc-classifier.md": "a6ab02b8f45f9d0b",
   "agents/gsd-doc-synthesizer.md": "fd3c18addbc8265d",
   "agents/gsd-doc-verifier.md": "e51e50892963ccc7",
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "134f83886c343733",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "23d7a3bb15bc8b7c",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/windsurf.json b/tests/fixtures/golden-install-parity/windsurf.json
index 18feb7adb..de7340f16 100644
--- a/tests/fixtures/golden-install-parity/windsurf.json
+++ b/tests/fixtures/golden-install-parity/windsurf.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "efc0d2dee321c654",
   "agents/gsd-codebase-mapper.md": "cfa2bbfaf264e1fd",
   "agents/gsd-debug-session-manager.md": "7ea9975264a99b2c",
-  "agents/gsd-debugger.md": "778496a47881df83",
+  "agents/gsd-debugger.md": "520dbc9408761e2e",
   "agents/gsd-doc-classifier.md": "a6ab02b8f45f9d0b",
   "agents/gsd-doc-synthesizer.md": "fd3c18addbc8265d",
   "agents/gsd-doc-verifier.md": "ede2f297b73b5a86",
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md": "580287399ad3ba68",
   "gsd-core/references/debugger-fix-acceptance.md": "ddd00cbd78dd3fdf",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "071651eaf7414a4c",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "883d0a1b9d9ff96e",
   "gsd-core/references/domain-probes.md": "762b965e84035b72",
diff --git a/tests/fixtures/golden-install-parity/zcode.json b/tests/fixtures/golden-install-parity/zcode.json
index fb88e1a66..3ef40c8db 100644
--- a/tests/fixtures/golden-install-parity/zcode.json
+++ b/tests/fixtures/golden-install-parity/zcode.json
@@ -8,7 +8,7 @@
   "agents/gsd-code-reviewer.md": "7d94fe8bfa6661aa",
   "agents/gsd-codebase-mapper.md": "7cc9d387f29c46e1",
   "agents/gsd-debug-session-manager.md": "716e31255a94e0ce",
-  "agents/gsd-debugger.md": "be00f854f4b0a6c9",
+  "agents/gsd-debugger.md": "376cb361acbafafd",
   "agents/gsd-doc-classifier.md": "146acf4d176134b5",
   "agents/gsd-doc-synthesizer.md": "b1f5e2eb28fa3659",
   "agents/gsd-doc-verifier.md": "7ed4d9611f678a95",
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md": "ce73e57d053ab8a7",
   "gsd-core/references/debugger-fix-acceptance.md": "5616622f33e00436",
   "gsd-core/references/debugger-philosophy.md": "0466f95a3d6bfcd3",
+  "gsd-core/references/debugger-sbfl.md": "a7d0cd5940d6d2cd",
   "gsd-core/references/decimal-phase-calculation.md": "46b5ba045852c474",
   "gsd-core/references/doc-conflict-engine.md": "67d019d23e17f934",
   "gsd-core/references/domain-probes.md": "62d23ed1992c48a9",
diff --git a/tests/fixtures/install-tree/antigravity.json b/tests/fixtures/install-tree/antigravity.json
index 087ad7905..d10828ff7 100644
--- a/tests/fixtures/install-tree/antigravity.json
+++ b/tests/fixtures/install-tree/antigravity.json
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/augment.json b/tests/fixtures/install-tree/augment.json
index ffe7d8d10..8f3c7a9e7 100644
--- a/tests/fixtures/install-tree/augment.json
+++ b/tests/fixtures/install-tree/augment.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/claude-local.json b/tests/fixtures/install-tree/claude-local.json
index e876f542e..531a4eb0c 100644
--- a/tests/fixtures/install-tree/claude-local.json
+++ b/tests/fixtures/install-tree/claude-local.json
@@ -132,6 +132,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/claude.json b/tests/fixtures/install-tree/claude.json
index 475259c19..3f7e4746e 100644
--- a/tests/fixtures/install-tree/claude.json
+++ b/tests/fixtures/install-tree/claude.json
@@ -61,6 +61,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/cline.json b/tests/fixtures/install-tree/cline.json
index 8a2a76c8d..018cdcf26 100644
--- a/tests/fixtures/install-tree/cline.json
+++ b/tests/fixtures/install-tree/cline.json
@@ -65,6 +65,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/codebuddy.json b/tests/fixtures/install-tree/codebuddy.json
index f5c919960..14e8f1a87 100644
--- a/tests/fixtures/install-tree/codebuddy.json
+++ b/tests/fixtures/install-tree/codebuddy.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/codex.json b/tests/fixtures/install-tree/codex.json
index fa1ab2eaa..99e756335 100644
--- a/tests/fixtures/install-tree/codex.json
+++ b/tests/fixtures/install-tree/codex.json
@@ -168,6 +168,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/copilot.json b/tests/fixtures/install-tree/copilot.json
index 201b73f6c..6fcf66339 100644
--- a/tests/fixtures/install-tree/copilot.json
+++ b/tests/fixtures/install-tree/copilot.json
@@ -63,6 +63,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/cursor.json b/tests/fixtures/install-tree/cursor.json
index d8484dc83..c11bd418e 100644
--- a/tests/fixtures/install-tree/cursor.json
+++ b/tests/fixtures/install-tree/cursor.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/hermes.json b/tests/fixtures/install-tree/hermes.json
index 997964f6c..5b3d192e6 100644
--- a/tests/fixtures/install-tree/hermes.json
+++ b/tests/fixtures/install-tree/hermes.json
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/kilo.json b/tests/fixtures/install-tree/kilo.json
index 70b883846..01d454ef8 100644
--- a/tests/fixtures/install-tree/kilo.json
+++ b/tests/fixtures/install-tree/kilo.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/kimi.json b/tests/fixtures/install-tree/kimi.json
index 6e19b8b8b..410bd83eb 100644
--- a/tests/fixtures/install-tree/kimi.json
+++ b/tests/fixtures/install-tree/kimi.json
@@ -126,6 +126,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/opencode.json b/tests/fixtures/install-tree/opencode.json
index 7b2a4fc03..bbd7223ea 100644
--- a/tests/fixtures/install-tree/opencode.json
+++ b/tests/fixtures/install-tree/opencode.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/pi.json b/tests/fixtures/install-tree/pi.json
index 06e7dcb07..a41a00c29 100644
--- a/tests/fixtures/install-tree/pi.json
+++ b/tests/fixtures/install-tree/pi.json
@@ -29,6 +29,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/qwen.json b/tests/fixtures/install-tree/qwen.json
index 5535bfb7b..eb66d94f8 100644
--- a/tests/fixtures/install-tree/qwen.json
+++ b/tests/fixtures/install-tree/qwen.json
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/trae.json b/tests/fixtures/install-tree/trae.json
index 57cb21e7d..d4762326e 100644
--- a/tests/fixtures/install-tree/trae.json
+++ b/tests/fixtures/install-tree/trae.json
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/windsurf.json b/tests/fixtures/install-tree/windsurf.json
index b6dd1fb8d..7c4c36870 100644
--- a/tests/fixtures/install-tree/windsurf.json
+++ b/tests/fixtures/install-tree/windsurf.json
@@ -62,6 +62,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",
diff --git a/tests/fixtures/install-tree/zcode.json b/tests/fixtures/install-tree/zcode.json
index ef56440b9..ce7ab9262 100644
--- a/tests/fixtures/install-tree/zcode.json
+++ b/tests/fixtures/install-tree/zcode.json
@@ -133,6 +133,7 @@
   "gsd-core/references/continuation-format.md",
   "gsd-core/references/debugger-fix-acceptance.md",
   "gsd-core/references/debugger-philosophy.md",
+  "gsd-core/references/debugger-sbfl.md",
   "gsd-core/references/decimal-phase-calculation.md",
   "gsd-core/references/doc-conflict-engine.md",
   "gsd-core/references/domain-probes.md",