Fix typed Context Builder prompt handoff (#526)

Scripts/Fixtures/test-suite-contract-ledger.tsv

@@ -1184,13 +1184,15 @@ root/RepoPromptTests.ContextBuilderFollowUpFinalizationMonitorTests/testStalledF
 root/RepoPromptTests.ContextBuilderFollowUpFinalizationMonitorTests/testTimeoutOutcomeWinsWhenCancellationAlsoCompletesFinalization	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderFollowUpFinalizationMonitorTests.swift	RepoPromptTests.ContextBuilderFollowUpFinalizationMonitorTests	testTimeoutOutcomeWinsWhenCancellationAlsoCompletesFinalization	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.000000			unreviewed	retain_pending_review		0	initial census source line 94
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testCommitAndClearTabContextReportsPersistenceSubphasesInOrder	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testCommitAndClearTabContextReportsPersistenceSubphasesInOrder	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.190000			unreviewed	retain_pending_review		0	initial census source line 371
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testContextBuilderToolProviderReportsDiscoveryAndGenerationStageEnvelope	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testContextBuilderToolProviderReportsDiscoveryAndGenerationStageEnvelope	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.154000			unreviewed	retain_pending_review		0	initial census source line 266
+root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testContextBuilderToolProviderUsesCallerPromptWithoutMutatingDiscoveryFallback	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testContextBuilderToolProviderUsesCallerPromptWithoutMutatingDiscoveryFallback	ContextBuilder	context_builder.typed_prompt.request_local_handoff	prompt_authority,state_preservation,hidden_guidance	integration_regression	root_swiftpm	routine	1		Injected follow-up and returned prompt contain caller task/context without discovery guidance or discovery output while the canonical tab retains its committed fallback.	Typed MCP responses from empty tabs could fail, leak discovery-only guidance, execute discovery prose, or overwrite canonical tab state.	0.524000		singleton_window_registry	window_state	retain		0	request-local typed prompt handoff across provider execution and result packaging
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testDeferredRunMappingSurvivesCommitUntilCallerCleanup	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testDeferredRunMappingSurvivesCommitUntilCallerCleanup	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.048000			unreviewed	retain_pending_review		0	initial census source line 425
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testPhaseCatalogCoversExpectedDiscoveryAndGenerationSequence	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testPhaseCatalogCoversExpectedDiscoveryAndGenerationSequence	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.000000			unreviewed	retain_pending_review		0	initial census source line 6
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testResponseDispositionRoutesRequestedModesAndFailsClosedOnMissingFollowUpState	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testResponseDispositionRoutesRequestedModesAndFailsClosedOnMissingFollowUpState	ContextBuilder	completion_routing		focused	root_swiftpm	routine	9		regression	retain	0.000000			stable	retain		0	committed snapshot response routing and fail-closed follow-up state
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testRunMCPPlanOrQuestionReportsProductionPhaseSequenceThroughFinalization	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testRunMCPPlanOrQuestionReportsProductionPhaseSequenceThroughFinalization	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.229000			unreviewed	retain_pending_review		0	initial census source line 166
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testSoftStageBoundEmitsOnceWithoutFailingTimeline	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testSoftStageBoundEmitsOnceWithoutFailingTimeline	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.001500			unreviewed	retain_pending_review		0	initial census source line 139
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testSuspendingSinkPreservesEveryTimedTransitionWhenItReentersTimeline	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testSuspendingSinkPreservesEveryTimedTransitionWhenItReentersTimeline	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.000500			unreviewed	retain_pending_review		0	initial census source line 66
 root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testTimelineEmitsTimedTransitionsAndUsesCurrentSubphaseForHeartbeat	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testTimelineEmitsTimedTransitionsAndUsesCurrentSubphaseForHeartbeat	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.000500			unreviewed	retain_pending_review		0	initial census source line 28
+root/RepoPromptTests.ContextBuilderMCPProgressTimelineTests/testTypedPromptResolverEnforcesPrecedenceAndReservedMarkupGrammar	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderMCPProgressTimelineTests.swift	RepoPromptTests.ContextBuilderMCPProgressTimelineTests	testTypedPromptResolverEnforcesPrecedenceAndReservedMarkupGrammar	ContextBuilder	context_builder.typed_prompt.resolution	prompt_precedence,lazy_sanitization,reserved_markup	parser_boundary	root_swiftpm	routine	16		Table assertions prove committed-prompt precedence, exact lowercase sibling removal, quote-aware attribute rejection, malformed reserved-markup rejection, and caller fallback into typed generation.	Malformed or hidden discovery guidance could reach typed generation, or valid committed prompts could be rejected.	0.001000			test_case	retain		0	request-local prompt authority and fail-closed reserved-markup grammar
 root/RepoPromptTests.ContextBuilderModelStartupSelectionTests/testCachedCLIFlagIsNotReadyUntilCurrentProcessVerification	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderModelStartupSelectionTests.swift	RepoPromptTests.ContextBuilderModelStartupSelectionTests	testCachedCLIFlagIsNotReadyUntilCurrentProcessVerification	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.001000			unreviewed	retain_pending_review		0	initial census source line 307
 root/RepoPromptTests.ContextBuilderModelStartupSelectionTests/testCursorStartupReadinessJoinsRunningPollWithoutDynamicMetadata	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderModelStartupSelectionTests.swift	RepoPromptTests.ContextBuilderModelStartupSelectionTests	testCursorStartupReadinessJoinsRunningPollWithoutDynamicMetadata	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.002000			unreviewed	retain_pending_review		0	initial census source line 259
 root/RepoPromptTests.ContextBuilderModelStartupSelectionTests/testDynamicPersistedSelectionSurvivesAfterACPDiscovery	root	Tests/RepoPromptTests/ContextBuilder/ContextBuilderModelStartupSelectionTests.swift	RepoPromptTests.ContextBuilderModelStartupSelectionTests	testDynamicPersistedSelectionSurvivesAfterACPDiscovery	ContextBuilder	unreviewed		unreviewed	root_swiftpm	routine	1		unreviewed	unreviewed	0.001000			unreviewed	retain_pending_review		0	initial census source line 145

Sources/RepoPrompt/Infrastructure/MCP/WindowTools/MCPContextBuilderToolProvider.swift

@@ -92,10 +92,102 @@ private struct ContextBuilderToolResult: Codable {
 
 enum ContextBuilderResponseDisposition {
     case contextOnly
-    case generate(HeadlessMode)
+    case generate(HeadlessMode, prompt: String)
     case failed(String)
 }
 
+enum ContextBuilderTypedPromptResolver {
+    private static let openingTag = "<discovery_agent-guidelines>"
+    private static let closingTag = "</discovery_agent-guidelines>"
+    private static let reservedName = "discovery_agent-guidelines"
+
+    static func resolve(
+        effectivePrompt: String,
+        usedAgentOutputAsPrompt: Bool,
+        callerInstructions: String
+    ) -> String? {
+        if !usedAgentOutputAsPrompt,
+           !effectivePrompt.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty
+        {
+            return effectivePrompt
+        }
+        return sanitizeCallerInstructions(callerInstructions)
+    }
+
+    private static func sanitizeCallerInstructions(_ instructions: String) -> String? {
+        var sanitized = ""
+        var cursor = instructions.startIndex
+        var insideGuidelines = false
+
+        while cursor < instructions.endIndex {
+            guard instructions[cursor] == "<" else {
+                if !insideGuidelines {
+                    sanitized.append(instructions[cursor])
+                }
+                cursor = instructions.index(after: cursor)
+                continue
+            }
+
+            guard let closingAngle = closingAngleIndex(in: instructions, after: cursor) else {
+                let remainder = instructions[cursor...]
+                guard remainder.range(of: reservedName, options: .caseInsensitive) == nil else {
+                    return nil
+                }
+                if !insideGuidelines {
+                    sanitized.append(contentsOf: remainder)
+                }
+                break
+            }
+
+            let afterTag = instructions.index(after: closingAngle)
+            let tag = instructions[cursor ..< afterTag]
+            if tag == openingTag {
+                guard !insideGuidelines else { return nil }
+                insideGuidelines = true
+            } else if tag == closingTag {
+                guard insideGuidelines else { return nil }
+                insideGuidelines = false
+            } else {
+                // Quote-aware tokenization keeps reserved markup inside attributes from becoming removable blocks.
+                guard tag.range(of: reservedName, options: .caseInsensitive) == nil else {
+                    return nil
+                }
+                if !insideGuidelines {
+                    sanitized.append(contentsOf: tag)
+                }
+            }
+            cursor = afterTag
+        }
+
+        guard !insideGuidelines else { return nil }
+        let result = sanitized.trimmingCharacters(in: .whitespacesAndNewlines)
+        return result.isEmpty ? nil : result
+    }
+
+    private static func closingAngleIndex(
+        in instructions: String,
+        after openingAngle: String.Index
+    ) -> String.Index? {
+        var cursor = instructions.index(after: openingAngle)
+        var activeQuote: Character?
+
+        while cursor < instructions.endIndex {
+            let character = instructions[cursor]
+            if let quote = activeQuote {
+                if character == quote {
+                    activeQuote = nil
+                }
+            } else if character == "\"" || character == "'" {
+                activeQuote = character
+            } else if character == ">" {
+                return cursor
+            }
+            cursor = instructions.index(after: cursor)
+        }
+        return nil
+    }
+}
+
 @MainActor
 final class MCPContextBuilderToolProvider: MCPWindowToolProviding {
     let group: MCPWindowToolGroup = .contextBuilder
@@ -444,15 +536,18 @@ final class MCPContextBuilderToolProvider: MCPWindowToolProviding {
                     responseType: responseType,
                     terminalDisposition: snapshot.terminalDisposition,
                     usedAgentOutputAsPrompt: snapshot.usedAgentOutputAsPrompt,
-                    effectivePrompt: effectivePrompt
+                    effectivePrompt: effectivePrompt,
+                    callerInstructions: instructions
                 )
+                var resultPrompt = effectivePrompt
 
                 switch responseDisposition {
                 case .contextOnly:
                     break
                 case let .failed(message):
                     throw MCPError.internalError(message)
-                case let .generate(mode):
+                case let .generate(mode, prompt):
+                    resultPrompt = prompt
                     try Task.checkCancellation()
                     let finalReviewAuthorization: ContextBuilderFinalReviewAuthorization?
                     if mode == .review, let workspaceContext {
@@ -543,7 +638,7 @@ final class MCPContextBuilderToolProvider: MCPWindowToolProviding {
                                 tabResolution.agentModeSessionID,
                                 tabResolution.agentModeRunID,
                                 mode,
-                                effectivePrompt,
+                                prompt,
                                 sel,
                                 lookupContext,
                                 tabResolution.reviewGitContext,
@@ -586,7 +681,7 @@ final class MCPContextBuilderToolProvider: MCPWindowToolProviding {
                     ContextBuilderToolResult(
                         tabID: resultTab.id.uuidString,
                         status: status,
-                        prompt: effectivePrompt,
+                        prompt: resultPrompt,
                         fileCount: fileCount,
                         totalTokens: normalizedTokens,
                         userTotalTokens: userTotalTokens,
@@ -652,28 +747,28 @@ final class MCPContextBuilderToolProvider: MCPWindowToolProviding {
         responseType: ContextBuilderResponseType?,
         terminalDisposition: ContextBuilderRunTerminalOutcome,
         usedAgentOutputAsPrompt: Bool,
-        effectivePrompt: String
+        effectivePrompt: String,
+        callerInstructions: String
     ) -> ContextBuilderResponseDisposition {
         guard responseType?.wantsResponse == true else { return .contextOnly }
 
         switch terminalDisposition {
         case .cancelled, .failed:
             return .contextOnly
         case .completed:
-            guard !usedAgentOutputAsPrompt else {
-                return .failed(
-                    "Context Builder completed without a typed direct response for the requested \(responseType?.rawValue ?? "response")"
-                )
-            }
-            guard !effectivePrompt.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty else {
+            guard let prompt = ContextBuilderTypedPromptResolver.resolve(
+                effectivePrompt: effectivePrompt,
+                usedAgentOutputAsPrompt: usedAgentOutputAsPrompt,
+                callerInstructions: callerInstructions
+            ) else {
                 return .failed(
                     "Context Builder completed without a prompt for the requested \(responseType?.rawValue ?? "response")"
                 )
             }
             guard let mode = responseType?.headlessMode else {
                 return .failed("Context Builder requested response mode is unavailable")
             }
-            return .generate(mode)
+            return .generate(mode, prompt: prompt)
         }
     }