diff --git a/src/resources/extensions/gsd/auto-prompts.ts b/src/resources/extensions/gsd/auto-prompts.ts
index a191abe8c..43b61bd2e 100644
--- a/src/resources/extensions/gsd/auto-prompts.ts
+++ b/src/resources/extensions/gsd/auto-prompts.ts
@@ -261,7 +261,12 @@ export async function inlineGsdRootFile(
 
 /**
  * Inline decisions with optional milestone scoping from the DB.
- * Falls back to filesystem via inlineGsdRootFile when DB unavailable or empty.
+ * Falls back to filesystem via inlineGsdRootFile only when DB is unavailable.
+ *
+ * Cascade logic (R005):
+ * 1. Query with { milestoneId, scope } if scope provided
+ * 2. If empty AND scope was provided, retry with { milestoneId } only (drop scope)
+ * 3. If still empty, return null (intentional per D020)
  */
 export async function inlineDecisionsFromDb(
   base: string, milestoneId?: string, scope?: string, level?: InlineLevel,
@@ -271,7 +276,15 @@ export async function inlineDecisionsFromDb(
     const { isDbAvailable } = await import("./gsd-db.js");
     if (isDbAvailable()) {
       const { queryDecisions, formatDecisionsForPrompt } = await import("./context-store.js");
-      const decisions = queryDecisions({ milestoneId, scope });
+
+      // First query: try with both milestoneId and scope (if scope provided)
+      let decisions = queryDecisions({ milestoneId, scope });
+
+      // Cascade: if empty AND scope was provided, retry without scope
+      if (decisions.length === 0 && scope) {
+        decisions = queryDecisions({ milestoneId });
+      }
+
       if (decisions.length > 0) {
         // Use compact format for non-full levels to save ~35% tokens
         const formatted = inlineLevel !== "full"
@@ -279,26 +292,29 @@ export async function inlineDecisionsFromDb(
           : formatDecisionsForPrompt(decisions);
         return `### Decisions\nSource: \`.gsd/DECISIONS.md\`\n\n${formatted}`;
       }
+      // DB available but cascade returned empty — intentional per D020, don't fall back to file
+      return null;
     }
   } catch (err) {
     logWarning("prompt", `inlineDecisionsFromDb failed: ${err instanceof Error ? err.message : String(err)}`);
   }
+  // DB unavailable — fall back to filesystem
   return inlineGsdRootFile(base, "decisions.md", "Decisions");
 }
 
 /**
- * Inline requirements with optional slice scoping from the DB.
+ * Inline requirements with optional milestone and slice scoping from the DB.
  * Falls back to filesystem via inlineGsdRootFile when DB unavailable or empty.
  */
 export async function inlineRequirementsFromDb(
-  base: string, sliceId?: string, level?: InlineLevel,
+  base: string, milestoneId?: string, sliceId?: string, level?: InlineLevel,
 ): Promise<string | null> {
   const inlineLevel = level ?? resolveInlineLevel();
   try {
     const { isDbAvailable } = await import("./gsd-db.js");
     if (isDbAvailable()) {
       const { queryRequirements, formatRequirementsForPrompt } = await import("./context-store.js");
-      const requirements = queryRequirements({ sliceId });
+      const requirements = queryRequirements({ milestoneId, sliceId });
       if (requirements.length > 0) {
         // Use compact format for non-full levels to save ~40% tokens
         const formatted = inlineLevel !== "full"
@@ -335,6 +351,131 @@ export async function inlineProjectFromDb(
   return inlineGsdRootFile(base, "project.md", "Project");
 }
 
+// ─── Stopwords for keyword extraction ─────────────────────────────────────
+const STOPWORDS = new Set(['of', 'the', 'and', 'a', 'for', '+', '-', 'to', 'in', 'on', 'with', 'is', 'as', 'by']);
+
+// Generic words that don't provide meaningful scope differentiation
+const GENERIC_WORDS = new Set([
+  'setup', 'integration', 'implementation', 'testing', 'test', 'tests',
+  'config', 'configuration', 'init', 'initial', 'basic', 'core',
+  'main', 'primary', 'final', 'complete', 'finish', 'end',
+  'start', 'begin', 'first', 'last', 'update', 'updates',
+  'fix', 'fixes', 'add', 'adds', 'remove', 'removes',
+  'create', 'creates', 'build', 'builds', 'deploy', 'deployment',
+  'refactor', 'refactoring', 'cleanup', 'polish', 'review',
+  // Process/activity words that describe what you're doing, not what domain
+  'hardening', 'validation', 'verification', 'optimization',
+  'improvement', 'enhancement', 'infrastructure',
+]);
+
+// Pattern to match slice/milestone/task IDs (e.g., S01, M001, T03)
+const UNIT_ID_PATTERN = /^[smt]\d+$/i;
+
+/**
+ * Derive a scope keyword from slice title and optional description.
+ * Returns the most specific noun (first non-generic keyword) for decision scoping.
+ *
+ * Examples:
+ * - "Auth Middleware & Protected Route" → "auth"
+ * - "Database & User Model Setup" → "database"
+ * - "Integration Testing" → undefined (too generic)
+ * - "API Rate Limiting" → "api"
+ *
+ * @param sliceTitle - The slice title
+ * @param sliceDescription - Optional roadmap description (demo text)
+ * @returns A single lowercase keyword or undefined if no meaningful scope
+ */
+export function deriveSliceScope(sliceTitle: string, sliceDescription?: string): string | undefined {
+  // Combine title and description for keyword extraction
+  const combinedText = sliceDescription
+    ? `${sliceTitle} ${sliceDescription}`
+    : sliceTitle;
+
+  // Extract all words, lowercase, remove punctuation
+  const words = combinedText
+    .split(/[\s&+,;:|/\\()-]+/)
+    .map(w => w.toLowerCase().replace(/[^a-z0-9]/g, ''))
+    .filter(w => w.length >= 2);
+
+  // Find the first word that is:
+  // 1. Not a stopword
+  // 2. Not a generic word
+  // 3. Not a unit ID (S01, M001, T03)
+  // 4. At least 3 characters (meaningful scope)
+  for (const word of words) {
+    if (STOPWORDS.has(word)) continue;
+    if (GENERIC_WORDS.has(word)) continue;
+    if (UNIT_ID_PATTERN.test(word)) continue;
+    if (word.length < 3) continue;
+    return word;
+  }
+
+  return undefined;
+}
+/**
+ * Extract keywords from a slice title for scoped knowledge queries.
+ * Splits on whitespace, filters stopwords, lowercases.
+ * Example: 'KNOWLEDGE scoping + roadmap excerpt' → ['knowledge', 'scoping', 'roadmap', 'excerpt']
+ */
+function extractKeywords(title: string): string[] {
+  return title
+    .split(/\s+/)
+    .map(w => w.toLowerCase().replace(/[^a-z0-9]/g, ''))
+    .filter(w => w.length > 0 && !STOPWORDS.has(w));
+}
+
+/**
+ * Inline scoped KNOWLEDGE.md content based on keywords from slice title.
+ * Reads KNOWLEDGE.md, filters to sections matching keywords, formats with header.
+ * Returns null if no KNOWLEDGE.md exists or no sections match.
+ */
+export async function inlineKnowledgeScoped(
+  base: string,
+  keywords: string[],
+): Promise<string | null> {
+  const knowledgePath = resolveGsdRootFile(base, "KNOWLEDGE");
+  if (!existsSync(knowledgePath)) return null;
+
+  const content = await loadFile(knowledgePath);
+  if (!content) return null;
+
+  // Import queryKnowledge from context-store
+  const { queryKnowledge } = await import("./context-store.js");
+  const scoped = await queryKnowledge(content, keywords);
+
+  // Return null if no sections matched (empty string from queryKnowledge)
+  if (!scoped) return null;
+
+  return `### Project Knowledge (scoped)\nSource: \`${relGsdRootFile("KNOWLEDGE")}\`\n\n${scoped.trim()}`;
+}
+
+/**
+ * Inline a roadmap excerpt for a specific slice.
+ * Reads full roadmap, extracts minimal excerpt with header + predecessor + target row.
+ * Returns null if roadmap doesn't exist or slice not found.
+ */
+export async function inlineRoadmapExcerpt(
+  base: string,
+  mid: string,
+  sid: string,
+): Promise<string | null> {
+  const roadmapPath = resolveMilestoneFile(base, mid, "ROADMAP");
+  if (!roadmapPath || !existsSync(roadmapPath)) return null;
+
+  const roadmapRel = relMilestoneFile(base, mid, "ROADMAP");
+  const content = await loadFile(roadmapPath);
+  if (!content) return null;
+
+  // Import formatRoadmapExcerpt from context-store
+  const { formatRoadmapExcerpt } = await import("./context-store.js");
+  const excerpt = formatRoadmapExcerpt(content, sid, roadmapRel);
+
+  // Return null if slice not found in roadmap
+  if (!excerpt) return null;
+
+  return `### Milestone Roadmap (excerpt)\nSource: \`${roadmapRel}\`\n\n${excerpt}`;
+}
+
 // ─── Skill Activation & Discovery ─────────────────────────────────────────
 
 function normalizeSkillReference(ref: string): string {
@@ -880,7 +1021,7 @@ export async function buildResearchMilestonePrompt(mid: string, midTitle: string
   inlined.push(await inlineFile(contextPath, contextRel, "Milestone Context"));
   const projectInline = await inlineProjectFromDb(base);
   if (projectInline) inlined.push(projectInline);
-  const requirementsInline = await inlineRequirementsFromDb(base);
+  const requirementsInline = await inlineRequirementsFromDb(base, mid);
   if (requirementsInline) inlined.push(requirementsInline);
   const decisionsInline = await inlineDecisionsFromDb(base, mid);
   if (decisionsInline) inlined.push(decisionsInline);
@@ -930,7 +1071,7 @@ export async function buildPlanMilestonePrompt(mid: string, midTitle: string, ba
   if (inlineLevel !== "minimal") {
     const projectInline = await inlineProjectFromDb(base);
     if (projectInline) inlined.push(projectInline);
-    const requirementsInline = await inlineRequirementsFromDb(base, undefined, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, undefined, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
     const decisionsInline = await inlineDecisionsFromDb(base, mid, undefined, inlineLevel);
     if (decisionsInline) inlined.push(decisionsInline);
@@ -999,19 +1140,35 @@ export async function buildResearchSlicePrompt(
   const sliceContextRel = relSliceFile(base, mid, sid, "CONTEXT");
 
   const inlined: string[] = [];
-  inlined.push(await inlineFile(roadmapPath, roadmapRel, "Milestone Roadmap"));
+
+  // Use roadmap excerpt instead of full roadmap for context reduction
+  const roadmapExcerptRS = await inlineRoadmapExcerpt(base, mid, sid);
+  if (roadmapExcerptRS) {
+    inlined.push(roadmapExcerptRS);
+  } else {
+    // Fall back to full roadmap if excerpt fails
+    inlined.push(await inlineFile(roadmapPath, roadmapRel, "Milestone Roadmap"));
+  }
+
   const contextInline = await inlineFileOptional(contextPath, contextRel, "Milestone Context");
   if (contextInline) inlined.push(contextInline);
   const sliceCtxInline = await inlineFileOptional(sliceContextPath, sliceContextRel, "Slice Context (from discussion)");
   if (sliceCtxInline) inlined.push(sliceCtxInline);
   const researchInline = await inlineFileOptional(milestoneResearchPath, milestoneResearchRel, "Milestone Research");
   if (researchInline) inlined.push(researchInline);
-  const decisionsInline = await inlineDecisionsFromDb(base, mid);
+
+  // Derive scope from slice title for decision filtering (R005)
+  const derivedScope = deriveSliceScope(sTitle);
+  const decisionsInline = await inlineDecisionsFromDb(base, mid, derivedScope);
   if (decisionsInline) inlined.push(decisionsInline);
-  const requirementsInline = await inlineRequirementsFromDb(base, sid);
+  const requirementsInline = await inlineRequirementsFromDb(base, mid, sid);
   if (requirementsInline) inlined.push(requirementsInline);
-  const knowledgeInlineRS = await inlineGsdRootFile(base, "knowledge.md", "Project Knowledge");
+
+  // Use scoped knowledge based on slice title keywords
+  const keywords = extractKeywords(sTitle);
+  const knowledgeInlineRS = await inlineKnowledgeScoped(base, keywords);
   if (knowledgeInlineRS) inlined.push(knowledgeInlineRS);
+
   inlined.push(inlineTemplate("research", "Research"));
 
   const depContent = await inlineDependencySummaries(mid, sid, base);
@@ -1060,19 +1217,33 @@ export async function buildPlanSlicePrompt(
   const researchSliceAnchor = readPhaseAnchor(base, mid, "research-slice");
   if (researchSliceAnchor) inlined.push(formatAnchorForPrompt(researchSliceAnchor));
 
-  inlined.push(await inlineFile(roadmapPath, roadmapRel, "Milestone Roadmap"));
+  // Use roadmap excerpt instead of full roadmap for context reduction
+  const roadmapExcerptPS = await inlineRoadmapExcerpt(base, mid, sid);
+  if (roadmapExcerptPS) {
+    inlined.push(roadmapExcerptPS);
+  } else {
+    // Fall back to full roadmap if excerpt fails
+    inlined.push(await inlineFile(roadmapPath, roadmapRel, "Milestone Roadmap"));
+  }
+
   const sliceCtxInline = await inlineFileOptional(sliceContextPath, sliceContextRel, "Slice Context (from discussion)");
   if (sliceCtxInline) inlined.push(sliceCtxInline);
   const researchInline = await inlineFileOptional(researchPath, researchRel, "Slice Research");
   if (researchInline) inlined.push(researchInline);
   if (inlineLevel !== "minimal") {
-    const decisionsInline = await inlineDecisionsFromDb(base, mid, undefined, inlineLevel);
+    // Derive scope from slice title for decision filtering (R005)
+    const derivedScopePS = deriveSliceScope(sTitle);
+    const decisionsInline = await inlineDecisionsFromDb(base, mid, derivedScopePS, inlineLevel);
     if (decisionsInline) inlined.push(decisionsInline);
-    const requirementsInline = await inlineRequirementsFromDb(base, sid, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, sid, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
   }
-  const knowledgeInlinePS = await inlineGsdRootFile(base, "knowledge.md", "Project Knowledge");
+
+  // Use scoped knowledge based on slice title keywords
+  const keywordsPS = extractKeywords(sTitle);
+  const knowledgeInlinePS = await inlineKnowledgeScoped(base, keywordsPS);
   if (knowledgeInlinePS) inlined.push(knowledgeInlinePS);
+
   inlined.push(inlineTemplate("plan", "Slice Plan"));
   if (inlineLevel === "full") {
     inlined.push(inlineTemplate("task-plan", "Task Plan"));
@@ -1272,7 +1443,7 @@ export async function buildCompleteSlicePrompt(
   if (sliceCtxInline) inlined.push(sliceCtxInline);
   inlined.push(await inlineFile(slicePlanPath, slicePlanRel, "Slice Plan"));
   if (inlineLevel !== "minimal") {
-    const requirementsInline = await inlineRequirementsFromDb(base, sid, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, sid, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
   }
   const knowledgeInlineCS = await inlineGsdRootFile(base, "knowledge.md", "Project Knowledge");
@@ -1355,7 +1526,7 @@ export async function buildCompleteMilestonePrompt(
 
   // Inline root GSD files (skip for minimal — completion can read these if needed)
   if (inlineLevel !== "minimal") {
-    const requirementsInline = await inlineRequirementsFromDb(base, undefined, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, undefined, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
     const decisionsInline = await inlineDecisionsFromDb(base, mid, undefined, inlineLevel);
     if (decisionsInline) inlined.push(decisionsInline);
@@ -1480,7 +1651,7 @@ export async function buildValidateMilestonePrompt(
 
   // Inline root GSD files
   if (inlineLevel !== "minimal") {
-    const requirementsInline = await inlineRequirementsFromDb(base, undefined, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, undefined, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
     const decisionsInline = await inlineDecisionsFromDb(base, mid, undefined, inlineLevel);
     if (decisionsInline) inlined.push(decisionsInline);
@@ -1656,7 +1827,7 @@ export async function buildReassessRoadmapPrompt(
   if (inlineLevel !== "minimal") {
     const projectInline = await inlineProjectFromDb(base);
     if (projectInline) inlined.push(projectInline);
-    const requirementsInline = await inlineRequirementsFromDb(base, undefined, inlineLevel);
+    const requirementsInline = await inlineRequirementsFromDb(base, mid, undefined, inlineLevel);
     if (requirementsInline) inlined.push(requirementsInline);
     const decisionsInline = await inlineDecisionsFromDb(base, mid, undefined, inlineLevel);
     if (decisionsInline) inlined.push(decisionsInline);
diff --git a/src/resources/extensions/gsd/context-store.ts b/src/resources/extensions/gsd/context-store.ts
index b23f1e855..df938555a 100644
--- a/src/resources/extensions/gsd/context-store.ts
+++ b/src/resources/extensions/gsd/context-store.ts
@@ -15,6 +15,7 @@ export interface DecisionQueryOpts {
 }
 
 export interface RequirementQueryOpts {
+  milestoneId?: string;
   sliceId?: string;
   status?: string;
 }
@@ -67,7 +68,8 @@ export function queryDecisions(opts?: DecisionQueryOpts): Decision[] {
 
 /**
  * Query active (non-superseded) requirements with optional filters.
- * - sliceId: filters where primary_owner LIKE '%sliceId%' OR supporting_slices LIKE '%sliceId%'
+ * - milestoneId: combined with sliceId for precise filtering (e.g. %M005/S01%)
+ * - sliceId: filters where primary_owner LIKE '%pattern%' OR supporting_slices LIKE '%pattern%'
  * - status: filters where status = :status (exact match)
  *
  * Returns [] if DB is not available. Never throws.
@@ -81,9 +83,19 @@ export function queryRequirements(opts?: RequirementQueryOpts): Requirement[] {
     const clauses: string[] = ['superseded_by IS NULL'];
     const params: Record<string, unknown> = {};
 
-    if (opts?.sliceId) {
+    // Combined milestone+slice filtering for precise scoping
+    if (opts?.milestoneId && opts?.sliceId) {
+      // Use combined pattern like %M005/S01% to avoid cross-milestone contamination
+      clauses.push('(primary_owner LIKE :combined_pattern OR supporting_slices LIKE :combined_pattern)');
+      params[':combined_pattern'] = `%${opts.milestoneId}/${opts.sliceId}%`;
+    } else if (opts?.sliceId) {
+      // Slice-only filtering (legacy behavior)
       clauses.push('(primary_owner LIKE :slice_pattern OR supporting_slices LIKE :slice_pattern)');
       params[':slice_pattern'] = `%${opts.sliceId}%`;
+    } else if (opts?.milestoneId) {
+      // Milestone-only filtering
+      clauses.push('(primary_owner LIKE :milestone_pattern OR supporting_slices LIKE :milestone_pattern)');
+      params[':milestone_pattern'] = `%${opts.milestoneId}%`;
     }
 
     if (opts?.status) {
@@ -194,3 +206,156 @@ export function queryArtifact(path: string): string | null {
 export function queryProject(): string | null {
   return queryArtifact('PROJECT.md');
 }
+
+// ─── Knowledge Query ───────────────────────────────────────────────────────
+
+/**
+ * Filter KNOWLEDGE.md sections by keyword matching.
+ * Uses H2 sections, matches keywords case-insensitively against:
+ * 1. Section header text
+ * 2. First paragraph of section content (up to first blank line or next heading)
+ *
+ * Per D020, returns empty string (not null) when no matches found.
+ * This signals "no relevant knowledge" vs "file not found".
+ *
+ * @param content - Full KNOWLEDGE.md content
+ * @param keywords - Keywords to match (case-insensitive)
+ * @returns Concatenated matching sections with H2 headers, or empty string
+ */
+export async function queryKnowledge(content: string, keywords: string[]): Promise<string> {
+  if (!content || keywords.length === 0) return '';
+
+  // Lazy import to avoid circular dependency
+  const { extractAllSections } = await import('./files.js');
+
+  const sections = extractAllSections(content, 2);
+  if (sections.size === 0) return '';
+
+  // Normalize keywords for case-insensitive matching
+  const normalizedKeywords = keywords.map(k => k.toLowerCase());
+
+  const matchingSections: string[] = [];
+
+  for (const [header, body] of sections) {
+    // Extract first paragraph: everything up to first blank line or next heading
+    const firstParagraph = body.split(/\n\s*\n|\n#/)[0] || '';
+
+    // Check if any keyword matches header or first paragraph
+    const headerLower = header.toLowerCase();
+    const paragraphLower = firstParagraph.toLowerCase();
+
+    const matches = normalizedKeywords.some(kw =>
+      headerLower.includes(kw) || paragraphLower.includes(kw)
+    );
+
+    if (matches) {
+      matchingSections.push(`## ${header}\n\n${body}`);
+    }
+  }
+
+  return matchingSections.join('\n\n');
+}
+
+// ─── Roadmap Excerpt Formatter ─────────────────────────────────────────────
+
+/**
+ * Format a minimal roadmap excerpt for prompt injection.
+ * Parses the slice table from roadmap content, extracts:
+ * 1. Header row + separator
+ * 2. Predecessor row (if sliceId depends on one via the Depends column)
+ * 3. Target slice row
+ * 4. Reference directive pointing to full roadmap path
+ *
+ * Per D021, this minimizes injected content while preserving dependency awareness.
+ * Returns empty string if sliceId is not found in the table.
+ * Never throws.
+ *
+ * @param roadmapContent - Full content of the M###-ROADMAP.md file
+ * @param sliceId - Target slice ID (e.g. 'S02')
+ * @param roadmapPath - Optional path for reference directive (defaults to generic)
+ */
+export function formatRoadmapExcerpt(
+  roadmapContent: string,
+  sliceId: string,
+  roadmapPath = 'ROADMAP.md',
+): string {
+  if (!roadmapContent || !sliceId) return '';
+
+  const lines = roadmapContent.split('\n');
+
+  // Find the slice table header: | ID | Slice | ... (case insensitive)
+  let headerIndex = -1;
+  for (let i = 0; i < lines.length; i++) {
+    const line = lines[i];
+    if (line && /^\s*\|\s*ID\s*\|\s*Slice\s*\|/i.test(line)) {
+      headerIndex = i;
+      break;
+    }
+  }
+
+  if (headerIndex === -1) return '';
+
+  // The separator should be the next line (|---|---|...)
+  const separatorIndex = headerIndex + 1;
+  if (separatorIndex >= lines.length) return '';
+
+  const headerLine = lines[headerIndex];
+  const separatorLine = lines[separatorIndex];
+
+  // Validate separator line looks like |---|---|... (may include : for alignment)
+  if (!separatorLine || !/^\s*\|[\s:\-|]+\|/.test(separatorLine)) return '';
+
+  // Parse table rows after separator
+  interface SliceRow {
+    line: string;
+    id: string;
+    depends: string;
+  }
+
+  const sliceRows: SliceRow[] = [];
+  for (let i = separatorIndex + 1; i < lines.length; i++) {
+    const line = lines[i];
+    if (!line || !line.trim().startsWith('|')) break; // End of table
+
+    // Parse row: | ID | Slice | Risk | Depends | Done | After this |
+    const cells = line.split('|').map(c => c.trim());
+    // cells[0] is empty (before first |), cells[1] is ID, etc.
+    if (cells.length < 5) continue;
+
+    const id = cells[1] || '';
+    const depends = cells[4] || ''; // Depends column (0-indexed: empty, ID, Slice, Risk, Depends, ...)
+
+    sliceRows.push({ line, id, depends });
+  }
+
+  // Find target slice row
+  const targetRow = sliceRows.find(r => r.id === sliceId);
+  if (!targetRow) return '';
+
+  // Find predecessor if target depends on one
+  // Depends column may contain: '—', 'S01', 'S01, S02', etc.
+  let predecessorRow: SliceRow | undefined;
+  const dependsRaw = targetRow.depends;
+  if (dependsRaw && dependsRaw !== '—' && dependsRaw !== '-') {
+    // Extract first dependency (e.g. 'S01' from 'S01, S02')
+    const depMatch = dependsRaw.match(/S\d+/);
+    if (depMatch) {
+      predecessorRow = sliceRows.find(r => r.id === depMatch[0]);
+    }
+  }
+
+  // Build excerpt
+  const excerptLines: string[] = [headerLine!, separatorLine!];
+
+  if (predecessorRow) {
+    excerptLines.push(predecessorRow.line);
+  }
+
+  excerptLines.push(targetRow.line);
+
+  // Add reference directive
+  excerptLines.push('');
+  excerptLines.push(`> See full roadmap: ${roadmapPath}`);
+
+  return excerptLines.join('\n');
+}
diff --git a/src/resources/extensions/gsd/tests/context-store.test.ts b/src/resources/extensions/gsd/tests/context-store.test.ts
index 88c1f84fd..f81934092 100644
--- a/src/resources/extensions/gsd/tests/context-store.test.ts
+++ b/src/resources/extensions/gsd/tests/context-store.test.ts
@@ -15,6 +15,8 @@ import {
   formatRequirementsForPrompt,
   queryArtifact,
   queryProject,
+  formatRoadmapExcerpt,
+  queryKnowledge,
 } from '../context-store.ts';
 
 // ═══════════════════════════════════════════════════════════════════════════
@@ -452,3 +454,177 @@ describe("context-store: queryProject", () => {
     assert.strictEqual(content, null, 'queryProject returns null when DB closed');
   });
 });
+
+// ═══════════════════════════════════════════════════════════════════════════
+// context-store: formatRoadmapExcerpt
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("context-store: formatRoadmapExcerpt", () => {
+  // Sample roadmap content matching actual M005-ROADMAP.md format
+  const sampleRoadmap = `# M005: Tiered Context Injection
+
+## Vision
+Refactor prompt builders to inject relevance-scoped context.
+
+## Slice Overview
+| ID | Slice | Risk | Depends | Done | After this |
+|----|-------|------|---------|------|------------|
+| S01 | Scope existing queries | low | — | ✅ | planSlice prompt scoped. |
+| S02 | KNOWLEDGE scoping | medium | S01 | ⬜ | KNOWLEDGE sections filtered. |
+| S03 | Measurement test | low | S02 | ⬜ | 40% reduction confirmed. |
+`;
+
+  test("S02 with S01 predecessor includes both rows", () => {
+    const result = formatRoadmapExcerpt(sampleRoadmap, 'S02', '.gsd/milestones/M005/M005-ROADMAP.md');
+
+    // Should have header
+    assert.match(result, /\| ID \| Slice \| Risk \| Depends \| Done \| After this \|/, 'has header row');
+    // Should have separator
+    assert.match(result, /\|----\|/, 'has separator row');
+    // Should have S01 predecessor
+    assert.match(result, /\| S01 \|/, 'has predecessor S01 row');
+    // Should have S02 target
+    assert.match(result, /\| S02 \|/, 'has target S02 row');
+    // Should have reference directive
+    assert.match(result, /See full roadmap:.*M005-ROADMAP\.md/, 'has reference directive');
+    // Should NOT have S03 (not relevant)
+    assert.ok(!result.includes('| S03 |'), 'does not include unrelated S03');
+  });
+
+  test("S01 with no predecessor includes only target row", () => {
+    const result = formatRoadmapExcerpt(sampleRoadmap, 'S01');
+
+    // Should have header + separator + S01 only
+    assert.match(result, /\| ID \| Slice \|/, 'has header row');
+    assert.match(result, /\| S01 \|/, 'has target S01 row');
+    // Should NOT have S02 or S03
+    assert.ok(!result.includes('| S02 |'), 'does not include S02');
+    assert.ok(!result.includes('| S03 |'), 'does not include S03');
+    // Should have reference
+    assert.match(result, /See full roadmap:/, 'has reference directive');
+
+    // Count rows: header + separator + S01 + blank + directive = 5 lines
+    const lines = result.split('\n');
+    assert.strictEqual(lines.length, 5, 'correct number of lines (no predecessor)');
+  });
+
+  test("missing slice returns empty string", () => {
+    const result = formatRoadmapExcerpt(sampleRoadmap, 'S99');
+
+    assert.strictEqual(result, '', 'missing slice returns empty string');
+  });
+
+  test("empty input returns empty string", () => {
+    assert.strictEqual(formatRoadmapExcerpt('', 'S01'), '', 'empty content returns empty');
+    assert.strictEqual(formatRoadmapExcerpt(sampleRoadmap, ''), '', 'empty sliceId returns empty');
+  });
+
+  test("handles table with various column formats", () => {
+    // Table with different spacing and content
+    const variantRoadmap = `# Milestone
+
+| ID | Slice | Risk | Depends | Done | After this |
+|:---|:------|:-----|:--------|:-----|:-----------|
+| S01 | First slice title | low | — | ✅ | First complete. |
+| S02 | Second longer slice title here | medium | S01 | ⬜ | Second working. |
+`;
+
+    const result = formatRoadmapExcerpt(variantRoadmap, 'S02');
+
+    assert.match(result, /\| S01 \|/, 'has predecessor with different spacing');
+    assert.match(result, /\| S02 \|/, 'has target with different spacing');
+    assert.match(result, /Second longer slice title/, 'preserves full slice title');
+  });
+
+  test("handles multiple dependencies by using first one", () => {
+    const multiDepRoadmap = `| ID | Slice | Risk | Depends | Done | After this |
+|----|-------|------|---------|------|------------|
+| S01 | First | low | — | ✅ | Done. |
+| S02 | Second | low | — | ✅ | Done. |
+| S03 | Third | medium | S01, S02 | ⬜ | Working. |
+`;
+
+    const result = formatRoadmapExcerpt(multiDepRoadmap, 'S03');
+
+    // Should include S01 (first dependency) and S03
+    assert.match(result, /\| S01 \|/, 'has first dependency S01');
+    assert.match(result, /\| S03 \|/, 'has target S03');
+    // S02 is also a dependency but we only include the first one
+    // (This is intentional to keep excerpts minimal)
+  });
+});
+
+// ═══════════════════════════════════════════════════════════════════════════
+// context-store: queryKnowledge
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("context-store: queryKnowledge", () => {
+  // Sample KNOWLEDGE.md content
+  const sampleKnowledge = `# Project Knowledge
+
+## Database Patterns
+SQLite is used with WAL mode for concurrent reads.
+Always use prepared statements.
+
+More database details here.
+
+## API Design
+REST endpoints follow OpenAPI spec.
+Use versioned paths like /v1/resource.
+
+## Testing Guidelines
+Unit tests use node:test.
+Integration tests mock external services.
+`;
+
+  test("single keyword matches header", async () => {
+    const result = await queryKnowledge(sampleKnowledge, ['database']);
+
+    assert.match(result, /## Database Patterns/, 'includes matching section header');
+    assert.match(result, /SQLite is used with WAL mode/, 'includes section content');
+    // Should NOT include other sections
+    assert.ok(!result.includes('## API Design'), 'does not include non-matching API section');
+    assert.ok(!result.includes('## Testing Guidelines'), 'does not include non-matching Testing section');
+  });
+
+  test("multiple keywords match multiple sections", async () => {
+    const result = await queryKnowledge(sampleKnowledge, ['database', 'testing']);
+
+    assert.match(result, /## Database Patterns/, 'includes Database section');
+    assert.match(result, /## Testing Guidelines/, 'includes Testing section');
+    assert.ok(!result.includes('## API Design'), 'does not include API section');
+  });
+
+  test("no matches returns empty string", async () => {
+    const result = await queryKnowledge(sampleKnowledge, ['nonexistent']);
+
+    assert.strictEqual(result, '', 'no matches returns empty string per D020');
+  });
+
+  test("keyword in first paragraph matches", async () => {
+    const result = await queryKnowledge(sampleKnowledge, ['sqlite']);
+
+    // 'sqlite' appears in first paragraph of Database Patterns
+    assert.match(result, /## Database Patterns/, 'matches keyword in first paragraph');
+    assert.match(result, /SQLite is used/, 'includes the section with matching paragraph');
+  });
+
+  test("case-insensitive matching", async () => {
+    const result = await queryKnowledge(sampleKnowledge, ['DATABASE', 'API']);
+
+    assert.match(result, /## Database Patterns/, 'case-insensitive header match');
+    assert.match(result, /## API Design/, 'case-insensitive header match for API');
+  });
+
+  test("empty keywords returns empty string", async () => {
+    const result = await queryKnowledge(sampleKnowledge, []);
+
+    assert.strictEqual(result, '', 'empty keywords returns empty string');
+  });
+
+  test("empty content returns empty string", async () => {
+    const result = await queryKnowledge('', ['database']);
+
+    assert.strictEqual(result, '', 'empty content returns empty string');
+  });
+});
diff --git a/src/resources/extensions/gsd/tests/decision-scope-cascade.test.ts b/src/resources/extensions/gsd/tests/decision-scope-cascade.test.ts
new file mode 100644
index 000000000..0660a771c
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/decision-scope-cascade.test.ts
@@ -0,0 +1,370 @@
+// decision-scope-cascade: Tests for R005 fallback cascade and scope derivation
+//
+// Validates:
+// (a) inlineDecisionsFromDb cascade: milestone + scope → milestone only → null
+// (b) deriveSliceScope extracts meaningful scope keywords from slice titles
+// (c) deriveSliceScope returns undefined for generic titles
+
+import { describe, test, afterEach, beforeEach } from "node:test";
+import assert from "node:assert/strict";
+import {
+  openDatabase,
+  closeDatabase,
+  isDbAvailable,
+  insertDecision,
+} from '../gsd-db.ts';
+import {
+  queryDecisions,
+  formatDecisionsForPrompt,
+} from '../context-store.ts';
+import { deriveSliceScope } from '../auto-prompts.ts';
+
+// ═══════════════════════════════════════════════════════════════════════════
+// deriveSliceScope: Extract meaningful scope from slice titles
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("deriveSliceScope: keyword extraction", () => {
+  test("extracts first meaningful noun from title", () => {
+    // "Auth Middleware & Protected Route" → "auth"
+    assert.strictEqual(
+      deriveSliceScope("Auth Middleware & Protected Route"),
+      "auth",
+      "extracts 'auth' from auth-related title",
+    );
+
+    // "Database & User Model Setup" → "database" (not "setup" which is generic)
+    const dbScope = deriveSliceScope("Database & User Model Setup");
+    assert.ok(
+      dbScope === "database" || dbScope === "user",
+      `expected 'database' or 'user', got '${dbScope}'`,
+    );
+
+    // "API Rate Limiting" → "api"
+    assert.strictEqual(
+      deriveSliceScope("API Rate Limiting"),
+      "api",
+      "extracts 'api' from API-related title",
+    );
+
+    // "Stripe Payment Integration" → "stripe"
+    assert.strictEqual(
+      deriveSliceScope("Stripe Payment Integration"),
+      "stripe",
+      "extracts 'stripe' from payment-related title",
+    );
+  });
+
+  test("returns undefined for generic titles", () => {
+    // "Integration Testing" → undefined (both words are generic)
+    assert.strictEqual(
+      deriveSliceScope("Integration Testing"),
+      undefined,
+      "returns undefined for generic 'Integration Testing'",
+    );
+
+    // "Setup & Configuration" → undefined (all generic)
+    assert.strictEqual(
+      deriveSliceScope("Setup & Configuration"),
+      undefined,
+      "returns undefined for generic 'Setup & Configuration'",
+    );
+
+    // "Final Review" → undefined
+    assert.strictEqual(
+      deriveSliceScope("Final Review"),
+      undefined,
+      "returns undefined for generic 'Final Review'",
+    );
+
+    // "Basic Implementation" → undefined
+    assert.strictEqual(
+      deriveSliceScope("Basic Implementation"),
+      undefined,
+      "returns undefined for generic 'Basic Implementation'",
+    );
+  });
+
+  test("handles description as additional context", () => {
+    // Generic title but specific description
+    const scope = deriveSliceScope(
+      "Initial Setup",
+      "Configure PostgreSQL database connection",
+    );
+    assert.ok(
+      scope === "postgresql" || scope === "database" || scope === "configure",
+      `expected meaningful scope from description, got '${scope}'`,
+    );
+  });
+
+  test("handles edge cases", () => {
+    // Empty title
+    assert.strictEqual(
+      deriveSliceScope(""),
+      undefined,
+      "returns undefined for empty title",
+    );
+
+    // Short words only
+    assert.strictEqual(
+      deriveSliceScope("A B C"),
+      undefined,
+      "returns undefined for very short words",
+    );
+
+    // Mixed case and punctuation
+    assert.strictEqual(
+      deriveSliceScope("OAuth2 + JWT Authentication"),
+      "oauth2",
+      "handles mixed case and punctuation",
+    );
+  });
+
+  test("filters unit IDs (S01, M001, T03)", () => {
+    // "S01: Infrastructure" → undefined (S01 is a unit ID, infrastructure is generic)
+    assert.strictEqual(
+      deriveSliceScope("S01: Infrastructure"),
+      undefined,
+      "skips S01 ID and returns undefined for generic 'Infrastructure'",
+    );
+
+    // "M001 Setup" → undefined (M001 is a unit ID, setup is generic)
+    assert.strictEqual(
+      deriveSliceScope("M001 Setup"),
+      undefined,
+      "skips M001 ID and returns undefined for generic 'Setup'",
+    );
+
+    // "T03: Database Migration" → "database" (skips T03, returns meaningful word)
+    assert.strictEqual(
+      deriveSliceScope("T03: Database Migration"),
+      "database",
+      "skips T03 ID and returns 'database'",
+    );
+
+    // "S02 Auth Flow" → "auth" (skips S02, returns meaningful word)
+    assert.strictEqual(
+      deriveSliceScope("S02 Auth Flow"),
+      "auth",
+      "skips S02 ID and returns 'auth'",
+    );
+  });
+
+  test("filters process/activity words", () => {
+    // "Integration Testing + Hardening" → undefined (all generic/process words)
+    assert.strictEqual(
+      deriveSliceScope("Integration Testing + Hardening"),
+      undefined,
+      "returns undefined for 'Integration Testing + Hardening'",
+    );
+
+    // "Validation & Verification" → undefined (both are process words)
+    assert.strictEqual(
+      deriveSliceScope("Validation & Verification"),
+      undefined,
+      "returns undefined for 'Validation & Verification'",
+    );
+
+    // "Performance Optimization" → "performance" (optimization is generic, performance is domain)
+    assert.strictEqual(
+      deriveSliceScope("Performance Optimization"),
+      "performance",
+      "extracts 'performance' before generic 'optimization'",
+    );
+
+    // "Security Enhancement" → "security" (enhancement is generic, security is domain)
+    assert.strictEqual(
+      deriveSliceScope("Security Enhancement"),
+      "security",
+      "extracts 'security' before generic 'enhancement'",
+    );
+
+    // "WebSocket Delivery Pipeline" → "websocket"
+    assert.strictEqual(
+      deriveSliceScope("WebSocket Delivery Pipeline"),
+      "websocket",
+      "extracts 'websocket' from delivery pipeline title",
+    );
+
+    // "Prisma Schema + Migration" → "prisma"
+    assert.strictEqual(
+      deriveSliceScope("Prisma Schema + Migration"),
+      "prisma",
+      "extracts 'prisma' from schema migration title",
+    );
+  });
+});
+
+// ═══════════════════════════════════════════════════════════════════════════
+// inlineDecisionsFromDb cascade: R005 implementation
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("inlineDecisionsFromDb: cascade fallback (R005)", () => {
+  beforeEach(() => {
+    openDatabase(':memory:');
+  });
+
+  afterEach(() => {
+    closeDatabase();
+  });
+
+  test("cascade: scoped query returns scoped decisions when they exist", () => {
+    // Insert decisions with different scopes
+    insertDecision({
+      id: 'D001', when_context: 'M001/S01', scope: 'auth',
+      decision: 'use JWT', choice: 'JWT', rationale: 'standard',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+    insertDecision({
+      id: 'D002', when_context: 'M001/S02', scope: 'database',
+      decision: 'use PostgreSQL', choice: 'PostgreSQL', rationale: 'relational',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+    insertDecision({
+      id: 'D003', when_context: 'M001/S01', scope: 'architecture',
+      decision: 'use microservices', choice: 'microservices', rationale: 'scalable',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Query with scope 'auth' should return D001 only
+    const authDecisions = queryDecisions({ milestoneId: 'M001', scope: 'auth' });
+    assert.strictEqual(authDecisions.length, 1, 'scoped query returns 1 decision');
+    assert.strictEqual(authDecisions[0]?.id, 'D001', 'returns D001 for auth scope');
+
+    // Query with scope 'database' should return D002 only
+    const dbDecisions = queryDecisions({ milestoneId: 'M001', scope: 'database' });
+    assert.strictEqual(dbDecisions.length, 1, 'scoped query returns 1 decision');
+    assert.strictEqual(dbDecisions[0]?.id, 'D002', 'returns D002 for database scope');
+  });
+
+  test("cascade: milestone-only fallback when scoped query returns empty", () => {
+    // Insert decisions for M001 with generic scope (e.g. 'architecture')
+    insertDecision({
+      id: 'D001', when_context: 'M001/S01', scope: 'architecture',
+      decision: 'use microservices', choice: 'microservices', rationale: 'scalable',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+    insertDecision({
+      id: 'D002', when_context: 'M001/S02', scope: 'performance',
+      decision: 'use caching', choice: 'Redis', rationale: 'fast',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Query with scope 'auth' (no decisions with this scope) should return empty
+    const authDecisions = queryDecisions({ milestoneId: 'M001', scope: 'auth' });
+    assert.strictEqual(authDecisions.length, 0, 'scoped query for auth returns empty');
+
+    // Simulate cascade: fallback to milestone-only query
+    const milestoneDecisions = queryDecisions({ milestoneId: 'M001' });
+    assert.strictEqual(milestoneDecisions.length, 2, 'milestone-only query returns 2 decisions');
+    const ids = milestoneDecisions.map(d => d.id).sort();
+    assert.deepStrictEqual(ids, ['D001', 'D002'], 'milestone fallback returns all M001 decisions');
+  });
+
+  test("cascade: returns null when both scoped and milestone queries are empty", () => {
+    // Insert decisions only for M002
+    insertDecision({
+      id: 'D001', when_context: 'M002/S01', scope: 'auth',
+      decision: 'use OAuth', choice: 'OAuth2', rationale: 'standard',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Query M001 with scope should return empty (no M001 decisions at all)
+    const scopedDecisions = queryDecisions({ milestoneId: 'M001', scope: 'auth' });
+    assert.strictEqual(scopedDecisions.length, 0, 'scoped query returns empty');
+
+    // Fallback to milestone-only should also return empty (no M001 decisions)
+    const milestoneDecisions = queryDecisions({ milestoneId: 'M001' });
+    assert.strictEqual(milestoneDecisions.length, 0, 'milestone-only query returns empty');
+
+    // This scenario would result in null from inlineDecisionsFromDb
+    // (we can't directly test inlineDecisionsFromDb here without mocking fs)
+  });
+
+  test("cascade: demonstrates the full cascade behavior", () => {
+    // This test demonstrates the cascade logic that inlineDecisionsFromDb implements:
+    // 1. First try { milestoneId: 'M001', scope: 'payment' } → empty
+    // 2. Then try { milestoneId: 'M001' } → gets D001, D002
+    // 3. Return the milestone-level decisions
+
+    // Setup: decisions exist at milestone level but not for 'payment' scope
+    insertDecision({
+      id: 'D001', when_context: 'M001/S01', scope: 'architecture',
+      decision: 'use REST', choice: 'REST API', rationale: 'standard',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+    insertDecision({
+      id: 'D002', when_context: 'M001/S02', scope: 'security',
+      decision: 'use HTTPS', choice: 'TLS 1.3', rationale: 'secure',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Step 1: Query with scope 'payment' (no matches)
+    const paymentDecisions = queryDecisions({ milestoneId: 'M001', scope: 'payment' });
+    assert.strictEqual(paymentDecisions.length, 0, 'payment scope query returns empty');
+
+    // Step 2: Since scope was provided but returned empty, cascade to milestone-only
+    const milestoneDecisions = queryDecisions({ milestoneId: 'M001' });
+    assert.strictEqual(milestoneDecisions.length, 2, 'milestone fallback returns 2 decisions');
+
+    // Step 3: Format and verify content
+    const formatted = formatDecisionsForPrompt(milestoneDecisions);
+    assert.match(formatted, /D001/, 'formatted output includes D001');
+    assert.match(formatted, /D002/, 'formatted output includes D002');
+    assert.match(formatted, /architecture/, 'formatted output includes architecture scope');
+    assert.match(formatted, /security/, 'formatted output includes security scope');
+  });
+});
+
+// ═══════════════════════════════════════════════════════════════════════════
+// Integration: scope derivation feeds into cascade
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("integration: scope derivation with cascade", () => {
+  beforeEach(() => {
+    openDatabase(':memory:');
+  });
+
+  afterEach(() => {
+    closeDatabase();
+  });
+
+  test("derived scope finds matching decisions when they exist", () => {
+    // Insert decisions with 'auth' scope
+    insertDecision({
+      id: 'D001', when_context: 'M001/S01', scope: 'auth',
+      decision: 'use JWT', choice: 'JWT tokens', rationale: 'stateless',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Derive scope from slice title
+    const derivedScope = deriveSliceScope("Auth Middleware & Protected Routes");
+    assert.strictEqual(derivedScope, 'auth', 'derives auth scope from title');
+
+    // Query with derived scope should find the decision
+    const decisions = queryDecisions({ milestoneId: 'M001', scope: derivedScope });
+    assert.strictEqual(decisions.length, 1, 'scoped query finds matching decision');
+    assert.strictEqual(decisions[0]?.id, 'D001', 'finds the auth decision');
+  });
+
+  test("generic title triggers milestone-level fallback", () => {
+    // Insert decisions with various scopes
+    insertDecision({
+      id: 'D001', when_context: 'M001/S01', scope: 'architecture',
+      decision: 'use monolith', choice: 'monolith', rationale: 'simple',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+    insertDecision({
+      id: 'D002', when_context: 'M001/S02', scope: 'tooling',
+      decision: 'use TypeScript', choice: 'TypeScript', rationale: 'type safety',
+      revisable: 'yes', made_by: 'agent', superseded_by: null,
+    });
+
+    // Derive scope from generic slice title
+    const derivedScope = deriveSliceScope("Integration Testing");
+    assert.strictEqual(derivedScope, undefined, 'generic title returns undefined scope');
+
+    // Without a scope, query returns all milestone decisions
+    const decisions = queryDecisions({ milestoneId: 'M001', scope: derivedScope });
+    assert.strictEqual(decisions.length, 2, 'no scope filter returns all decisions');
+  });
+});
diff --git a/src/resources/extensions/gsd/tests/measurement.test.ts b/src/resources/extensions/gsd/tests/measurement.test.ts
new file mode 100644
index 000000000..25785d10f
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/measurement.test.ts
@@ -0,0 +1,531 @@
+import { describe, test } from "node:test";
+import assert from "node:assert/strict";
+import {
+  queryKnowledge,
+  formatRoadmapExcerpt,
+} from '../context-store.ts';
+
+// ═══════════════════════════════════════════════════════════════════════════
+// measurement.test.ts — Verify ≥40% context reduction from scoped injection
+//
+// Tests queryKnowledge() and formatRoadmapExcerpt() with realistic synthetic
+// fixtures to confirm the context reduction target is met.
+// ═══════════════════════════════════════════════════════════════════════════
+
+// ─── Synthetic KNOWLEDGE.md Fixture (~8KB, 9 H2 sections) ──────────────────
+
+const syntheticKnowledge = `# Project Knowledge Base
+
+## Database Patterns
+SQLite is the primary persistence layer, using WAL mode for concurrent reads.
+All queries use prepared statements for SQL injection prevention.
+Connection pooling is handled by better-sqlite3's synchronous API.
+Schema migrations are versioned and applied at startup.
+
+Example patterns:
+- Use transactions for multi-statement operations
+- Prefer RETURNING clause for insert/update
+- Index foreign keys for join performance
+- Use CHECK constraints for data validation
+
+Performance considerations:
+- WAL checkpoint every 1000 writes
+- Vacuum on shutdown for space reclamation
+- Page size 4096 for SSD optimization
+
+Database schema evolution:
+- Migrations stored in migrations/ directory
+- Each migration has up/down scripts
+- Version table tracks applied migrations
+- Rollback supported for last N migrations
+
+Connection management:
+- Single connection for write operations
+- Read connections pooled for concurrency
+- Connection timeout set to 5 seconds
+- Busy timeout handles lock contention
+
+Query patterns:
+- Use prepared statements for parameterization
+- Batch inserts via INSERT ... VALUES syntax
+- Upserts via INSERT OR REPLACE
+- Pagination via LIMIT/OFFSET or cursor
+
+## API Design Principles
+REST endpoints follow OpenAPI 3.0 specification.
+Versioned paths use /v1/resource pattern.
+Authentication uses Bearer tokens in Authorization header.
+Rate limiting applies per-client with sliding window algorithm.
+
+Response formats:
+- Success: { data: T, meta?: { pagination } }
+- Error: { error: { code, message, details? } }
+- Pagination: cursor-based for large collections
+
+Content negotiation:
+- Accept: application/json (default)
+- Accept: text/plain (for CLI consumers)
+- Accept: text/event-stream (for SSE endpoints)
+
+API versioning strategy:
+- Major versions in URL path (/v1, /v2)
+- Minor versions via Accept-Version header
+- Deprecation warnings in response headers
+- 12-month sunset period for old versions
+
+Endpoint naming conventions:
+- Nouns for resources (users, projects)
+- Verbs only for non-CRUD actions (login, export)
+- Plural form for collections
+- Singular for singletons (me, config)
+
+HTTP method semantics:
+- GET: read-only, cacheable
+- POST: create or non-idempotent action
+- PUT: full replacement
+- PATCH: partial update
+- DELETE: remove resource
+
+## Testing Strategy
+Unit tests use node:test with strict assertions.
+Integration tests mock external services via msw.
+E2E tests use Playwright for browser automation.
+Test coverage target is 80% line coverage.
+
+Test organization:
+- Unit tests adjacent to source files (*.test.ts)
+- Integration tests in __tests__/integration/
+- E2E tests in e2e/ directory
+- Fixtures in __fixtures__/ subdirectories
+
+Mocking guidelines:
+- Prefer dependency injection over global mocks
+- Use vi.mock() sparingly, only for ES module boundaries
+- Reset mocks in afterEach hooks
+
+Test data management:
+- Factories generate realistic test data
+- Seeds populate database for integration tests
+- Snapshots capture expected output
+- Golden files for complex comparisons
+
+Assertion patterns:
+- Use strict equality for primitives
+- Deep equality for objects/arrays
+- Regex matching for dynamic content
+- Snapshot testing for UI components
+
+Test isolation:
+- Each test gets fresh database state
+- Environment variables reset between tests
+- File system operations use temp directories
+- Network calls intercepted by mock server
+
+## Error Handling
+Errors are typed using discriminated unions.
+Application errors extend BaseError class.
+HTTP errors map to standard status codes.
+Unhandled rejections trigger graceful shutdown.
+
+Error codes follow domain prefixes:
+- AUTH_xxx: Authentication/authorization errors
+- DB_xxx: Database operation failures
+- NET_xxx: Network/external service errors
+- VAL_xxx: Validation errors
+
+Logging integration:
+- Error instances auto-serialize to JSON
+- Stack traces included in development
+- Correlation IDs propagate through request chain
+
+Error recovery strategies:
+- Retry with exponential backoff for transient errors
+- Circuit breaker for external service failures
+- Fallback values for non-critical operations
+- Graceful degradation for partial failures
+
+User-facing error messages:
+- Generic messages for security-sensitive errors
+- Actionable guidance for recoverable errors
+- Reference codes for support escalation
+- Localized messages via i18n
+
+Error boundary patterns:
+- Component-level boundaries in UI
+- Route-level error handlers in API
+- Global unhandled rejection handlers
+- Process-level crash recovery
+
+## Observability Patterns
+Structured logging uses pino with JSON output.
+Metrics collected via OpenTelemetry SDK.
+Traces propagate context through async boundaries.
+Health checks exposed at /health and /ready endpoints.
+
+Log levels:
+- ERROR: Unrecoverable failures
+- WARN: Degraded operation
+- INFO: Significant state changes
+- DEBUG: Detailed diagnostic data
+
+Metric types:
+- Counters for request counts
+- Histograms for latency distribution
+- Gauges for resource utilization
+
+Trace context propagation:
+- W3C Trace Context headers
+- Baggage for cross-service metadata
+- Span attributes for searchability
+- Events for significant moments
+
+Dashboard design:
+- SLO dashboards for reliability
+- Request flow visualization
+- Error rate trends
+- Resource saturation alerts
+
+Alerting strategy:
+- Page for customer-impacting issues
+- Ticket for degraded performance
+- Notification for capacity planning
+- Silence during maintenance windows
+
+## Security Guidelines
+Secrets never appear in logs or error messages.
+Environment variables validated at startup.
+CORS configured per-environment whitelist.
+CSP headers enforced for web responses.
+
+Input validation:
+- Zod schemas for request body parsing
+- Path parameters validated against patterns
+- Query parameters have default/max values
+
+Output encoding:
+- HTML entities escaped in templates
+- JSON stringification for API responses
+- URL encoding for redirect targets
+
+Authentication patterns:
+- JWT tokens with short expiry
+- Refresh token rotation
+- Session invalidation on logout
+- Multi-factor authentication support
+
+Authorization model:
+- Role-based access control (RBAC)
+- Resource-level permissions
+- Attribute-based policies (ABAC)
+- Principle of least privilege
+
+Secure communication:
+- TLS 1.3 minimum
+- Certificate pinning for mobile
+- HSTS preload list
+- Certificate transparency logging
+
+## Performance Optimization
+Critical paths target sub-10ms latency.
+Database queries use covering indexes.
+Response compression enabled for > 1KB bodies.
+Static assets served with immutable caching.
+
+Caching strategy:
+- Redis for session data
+- In-memory LRU for hot paths
+- CDN for static assets
+- Stale-while-revalidate for API responses
+
+Memory management:
+- Stream large payloads instead of buffering
+- Weak references for disposable caches
+- Manual GC hints for batch operations
+
+Query optimization:
+- Explain plans for complex queries
+- Index usage analysis
+- Query result caching
+- Connection pooling tuning
+
+Frontend performance:
+- Code splitting for lazy loading
+- Image optimization and lazy loading
+- Critical CSS inlining
+- Prefetching for likely navigations
+
+Backend performance:
+- Async I/O for non-blocking operations
+- Worker threads for CPU-bound tasks
+- Connection keep-alive
+- Response streaming
+
+## Deployment Architecture
+Containers built with multi-stage Dockerfiles.
+Kubernetes manifests in deploy/ directory.
+Horizontal pod autoscaling on CPU/memory.
+Rolling updates with zero-downtime.
+
+Environment hierarchy:
+- development: local Docker Compose
+- staging: shared k8s namespace
+- production: isolated k8s cluster
+
+Configuration:
+- ConfigMaps for non-sensitive config
+- Secrets for credentials
+- Environment-specific overlays via Kustomize
+
+Container best practices:
+- Non-root user in container
+- Read-only filesystem where possible
+- Resource limits and requests
+- Liveness and readiness probes
+
+Service mesh integration:
+- Istio for traffic management
+- mTLS for service-to-service auth
+- Retry and timeout policies
+- Circuit breaking configuration
+
+Disaster recovery:
+- Database replication across zones
+- Point-in-time recovery capability
+- Regular backup verification
+- Documented runbooks
+
+## Development Workflow
+Feature branches follow conventional commits.
+PRs require CI pass and code review.
+Main branch deploys to staging automatically.
+Release tags trigger production deployment.
+
+CI pipeline stages:
+1. Install dependencies
+2. Lint and type check
+3. Unit tests with coverage
+4. Build artifacts
+5. Integration tests
+6. Security scan
+
+Local development:
+- pnpm for package management
+- Turborepo for monorepo orchestration
+- Docker Compose for service dependencies
+
+Code review guidelines:
+- Focus on correctness and clarity
+- Security-sensitive changes require security review
+- Performance-critical paths need benchmarks
+- Breaking changes need migration guide
+
+Branch strategy:
+- main: production-ready code
+- develop: integration branch (optional)
+- feature/*: new functionality
+- fix/*: bug fixes
+- release/*: release preparation
+
+Documentation requirements:
+- README for project overview
+- API docs auto-generated from OpenAPI
+- Architecture decision records (ADRs)
+- Runbooks for operational procedures
+`;
+
+// ─── Synthetic Roadmap Fixture (~1KB, 4 slices) ────────────────────────────
+
+const syntheticRoadmap = `# M005: Tiered Context Injection
+
+## Vision
+Refactor prompt builders to inject relevance-scoped context instead of full files.
+This reduces token consumption and improves agent focus on relevant information.
+
+## Success Criteria
+- [ ] 40% reduction in injected context size
+- [ ] No regression in agent task completion rate
+- [ ] Measurable test confirms reduction target
+
+## Slice Overview
+| ID | Slice | Risk | Depends | Done | After this |
+|----|-------|------|---------|------|------------|
+| S01 | Scope existing DB queries | low | — | ✅ | planSlice and researchSlice use milestone+slice filters for decisions/requirements. |
+| S02 | KNOWLEDGE scoping + roadmap excerpt | medium | S01 | ⬜ | KNOWLEDGE sections filtered by keywords. Roadmap injected as excerpt. |
+| S03 | Measurement test suite | low | S02 | ⬜ | Automated tests confirm 40% reduction vs baseline. |
+| S04 | Documentation and rollout | low | S03 | ⬜ | Updated docs. Feature flag for gradual rollout. |
+
+## Key Risks
+1. Keyword extraction may miss relevant sections — mitigate with fallback to full content
+2. Excerpt parsing fragile to roadmap format changes — mitigate with graceful degradation
+
+## Definition of Done
+- [ ] All slices complete with passing verification
+- [ ] Measurement tests in CI
+- [ ] No increase in prompt build latency
+`;
+
+// ═══════════════════════════════════════════════════════════════════════════
+// Measurement Tests
+// ═══════════════════════════════════════════════════════════════════════════
+
+describe("measurement: context reduction verification", () => {
+  test("synthetic KNOWLEDGE fixture is ~8KB as specified", () => {
+    const sizeKB = syntheticKnowledge.length / 1024;
+    assert.ok(
+      sizeKB >= 7 && sizeKB <= 10,
+      `KNOWLEDGE fixture should be ~8KB, got ${sizeKB.toFixed(2)}KB`
+    );
+  });
+
+  test("synthetic KNOWLEDGE has 9 H2 sections", () => {
+    const h2Count = (syntheticKnowledge.match(/^## /gm) || []).length;
+    assert.strictEqual(h2Count, 9, `KNOWLEDGE fixture should have 9 H2 sections, got ${h2Count}`);
+  });
+
+  test("queryKnowledge achieves ≥40% reduction with targeted keywords", async () => {
+    // Keywords targeting 2 sections: "Database Patterns" and "Testing Strategy"
+    const keywords = ['database', 'testing'];
+    
+    const scopedResult = await queryKnowledge(syntheticKnowledge, keywords);
+    
+    const fullSize = syntheticKnowledge.length;
+    const scopedSize = scopedResult.length;
+    const reductionPct = ((fullSize - scopedSize) / fullSize) * 100;
+    
+    // Verify we got matching sections
+    assert.match(scopedResult, /## Database Patterns/, 'should include Database section');
+    assert.match(scopedResult, /## Testing Strategy/, 'should include Testing section');
+    
+    // Verify we excluded other sections
+    assert.ok(!scopedResult.includes('## API Design'), 'should exclude API section');
+    assert.ok(!scopedResult.includes('## Observability'), 'should exclude Observability section');
+    assert.ok(!scopedResult.includes('## Deployment'), 'should exclude Deployment section');
+    
+    // Verify ≥40% reduction (2/9 sections = ~78% reduction expected)
+    assert.ok(
+      reductionPct >= 40,
+      `queryKnowledge should achieve ≥40% reduction, got ${reductionPct.toFixed(1)}% (${scopedSize} chars vs ${fullSize} chars)`
+    );
+    
+    console.log(`  → queryKnowledge: ${reductionPct.toFixed(1)}% reduction (${scopedSize} → ${fullSize} chars)`);
+  });
+
+  test("queryKnowledge with single keyword achieves ≥40% reduction", async () => {
+    // Single keyword targeting 1 section
+    const keywords = ['security'];
+    
+    const scopedResult = await queryKnowledge(syntheticKnowledge, keywords);
+    
+    const fullSize = syntheticKnowledge.length;
+    const scopedSize = scopedResult.length;
+    const reductionPct = ((fullSize - scopedSize) / fullSize) * 100;
+    
+    // Verify we got matching section
+    assert.match(scopedResult, /## Security Guidelines/, 'should include Security section');
+    
+    // Verify ≥40% reduction (1/9 sections = ~89% reduction expected)
+    assert.ok(
+      reductionPct >= 40,
+      `single keyword should achieve ≥40% reduction, got ${reductionPct.toFixed(1)}%`
+    );
+  });
+
+  test("formatRoadmapExcerpt achieves ≥40% reduction", () => {
+    const sliceId = 'S02';
+    
+    const excerptResult = formatRoadmapExcerpt(syntheticRoadmap, sliceId, '.gsd/milestones/M005/M005-ROADMAP.md');
+    
+    const fullSize = syntheticRoadmap.length;
+    const excerptSize = excerptResult.length;
+    const reductionPct = ((fullSize - excerptSize) / fullSize) * 100;
+    
+    // Verify excerpt contains required elements
+    assert.match(excerptResult, /\| ID \| Slice \|/, 'should have table header');
+    assert.match(excerptResult, /\| S01 \|/, 'should have predecessor S01');
+    assert.match(excerptResult, /\| S02 \|/, 'should have target S02');
+    assert.match(excerptResult, /See full roadmap:/, 'should have reference directive');
+    
+    // Verify we excluded other slices
+    assert.ok(!excerptResult.includes('| S03 |'), 'should exclude S03');
+    assert.ok(!excerptResult.includes('| S04 |'), 'should exclude S04');
+    
+    // Verify ≥40% reduction (2 rows + overhead vs full roadmap = significant reduction)
+    assert.ok(
+      reductionPct >= 40,
+      `formatRoadmapExcerpt should achieve ≥40% reduction, got ${reductionPct.toFixed(1)}% (${excerptSize} chars vs ${fullSize} chars)`
+    );
+    
+    console.log(`  → formatRoadmapExcerpt: ${reductionPct.toFixed(1)}% reduction (${excerptSize} → ${fullSize} chars)`);
+  });
+
+  test("combined KNOWLEDGE + roadmap reduction exceeds 40%", async () => {
+    // Simulate what happens in buildPlanSlicePrompt
+    const keywords = ['database', 'testing'];
+    
+    const scopedKnowledge = await queryKnowledge(syntheticKnowledge, keywords);
+    const scopedRoadmap = formatRoadmapExcerpt(syntheticRoadmap, 'S02');
+    
+    const fullKnowledgeSize = syntheticKnowledge.length;
+    const fullRoadmapSize = syntheticRoadmap.length;
+    const fullTotal = fullKnowledgeSize + fullRoadmapSize;
+    
+    const scopedKnowledgeSize = scopedKnowledge.length;
+    const scopedRoadmapSize = scopedRoadmap.length;
+    const scopedTotal = scopedKnowledgeSize + scopedRoadmapSize;
+    
+    const combinedReductionPct = ((fullTotal - scopedTotal) / fullTotal) * 100;
+    
+    // Combined reduction should easily exceed 40%
+    assert.ok(
+      combinedReductionPct >= 40,
+      `combined reduction should be ≥40%, got ${combinedReductionPct.toFixed(1)}%`
+    );
+    
+    console.log(`  → Combined: ${combinedReductionPct.toFixed(1)}% reduction`);
+    console.log(`    - KNOWLEDGE: ${fullKnowledgeSize} → ${scopedKnowledgeSize} chars`);
+    console.log(`    - Roadmap: ${fullRoadmapSize} → ${scopedRoadmapSize} chars`);
+    console.log(`    - Total: ${fullTotal} → ${scopedTotal} chars`);
+  });
+});
+
+describe("measurement: edge cases maintain reduction target", () => {
+  test("three keywords still achieves ≥40% reduction", async () => {
+    // Even with 3 matching sections (3/9 = 33%), we should hit target
+    const keywords = ['database', 'api', 'security'];
+    
+    const scopedResult = await queryKnowledge(syntheticKnowledge, keywords);
+    
+    const fullSize = syntheticKnowledge.length;
+    const scopedSize = scopedResult.length;
+    const reductionPct = ((fullSize - scopedSize) / fullSize) * 100;
+    
+    // Verify matches (3 sections)
+    assert.match(scopedResult, /## Database Patterns/, 'should include Database');
+    assert.match(scopedResult, /## API Design/, 'should include API');
+    assert.match(scopedResult, /## Security Guidelines/, 'should include Security');
+    
+    // With 3/9 sections, reduction should be ~67%
+    assert.ok(
+      reductionPct >= 40,
+      `3 keywords should still achieve ≥40% reduction, got ${reductionPct.toFixed(1)}%`
+    );
+  });
+
+  test("excerpt for S01 (no dependencies) achieves ≥40% reduction", () => {
+    const excerptResult = formatRoadmapExcerpt(syntheticRoadmap, 'S01');
+    
+    const fullSize = syntheticRoadmap.length;
+    const excerptSize = excerptResult.length;
+    const reductionPct = ((fullSize - excerptSize) / fullSize) * 100;
+    
+    // S01 has no predecessor, so just 1 row + header + reference
+    assert.match(excerptResult, /\| S01 \|/, 'should have S01');
+    assert.ok(!excerptResult.includes('| S02 |'), 'should not have S02');
+    
+    // Single row should still achieve significant reduction
+    assert.ok(
+      reductionPct >= 40,
+      `S01 excerpt should achieve ≥40% reduction, got ${reductionPct.toFixed(1)}%`
+    );
+  });
+});