Add Java orchestrator to connect to the AI engine (#6003)

# Description of Changes
Add Java orchestration layer which can connect and go back and forth
with the AI engine to get results for the user. It's expected that the
AI engine will not be publicly available and this Java layer will always
be in front of it, to manage sessions and auth etc.

.gitignore

@@ -181,6 +181,7 @@ venv.bak/
 .idea/
 *.iml
 out/
+.junie/
 
 # Ignore Mac DS_Store files
 .DS_Store

app/common/src/main/java/stirling/software/common/model/ApplicationProperties.java

@@ -75,6 +75,7 @@ public class ApplicationProperties {
     private AutoPipeline autoPipeline = new AutoPipeline();
     private ProcessExecutor processExecutor = new ProcessExecutor();
     private PdfEditor pdfEditor = new PdfEditor();
+    private AiEngine aiEngine = new AiEngine();
 
     @Bean
     public PropertySource<?> dynamicYamlPropertySource(ConfigurableEnvironment environment)
@@ -231,6 +232,13 @@ public class ApplicationProperties {
         }
     }
 
+    @Data
+    public static class AiEngine {
+        private boolean enabled = false;
+        private String url = "http://localhost:5001";
+        private int timeoutSeconds = 120;
+    }
+
     @Data
     public static class Legal {
         private String termsAndConditions;

app/core/src/main/resources/settings.yml.template

@@ -325,6 +325,11 @@ processExecutor:
     ghostscriptTimeoutMinutes: 30
     ocrMyPdfTimeoutMinutes: 30
 
+aiEngine:
+  enabled: false # Set to 'true' to enable the AI engine integration
+  url: http://localhost:5001 # URL of the Python AI engine
+  timeoutSeconds: 120 # Timeout in seconds for AI engine requests
+
 pdfEditor:
   fallback-font: classpath:/static/fonts/NotoSans-Regular.ttf # Override to point at a custom fallback font
   cache:

app/proprietary/src/main/java/stirling/software/proprietary/controller/api/AiEngineController.java

@@ -0,0 +1,83 @@
+package stirling.software.proprietary.controller.api;
+
+import java.io.IOException;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestBody;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.server.ResponseStatusException;
+
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.tags.Tag;
+
+import jakarta.validation.Valid;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+import stirling.software.proprietary.model.api.ai.AiWorkflowRequest;
+import stirling.software.proprietary.model.api.ai.AiWorkflowResponse;
+import stirling.software.proprietary.service.AiEngineClient;
+import stirling.software.proprietary.service.AiWorkflowService;
+
+import tools.jackson.core.JacksonException;
+import tools.jackson.databind.JsonNode;
+import tools.jackson.databind.ObjectMapper;
+
+@Slf4j
+@RestController
+@RequestMapping("/api/v1/ai")
+@RequiredArgsConstructor
+@Tag(name = "AI Engine", description = "Endpoints for AI-powered PDF workflows")
+public class AiEngineController {
+
+    private final AiEngineClient aiEngineClient;
+    private final AiWorkflowService aiWorkflowService;
+    private final ObjectMapper objectMapper;
+
+    @GetMapping("/health")
+    @Operation(
+            summary = "AI engine health check",
+            description = "Returns the health status of the AI engine including configured models")
+    public ResponseEntity<String> health() throws IOException {
+        String response = aiEngineClient.get("/health");
+        return ResponseEntity.ok().contentType(MediaType.APPLICATION_JSON).body(response);
+    }
+
+    @PostMapping(value = "/orchestrate", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
+    @Operation(
+            summary = "Run an AI workflow against a PDF",
+            description =
+                    "Accepts a PDF upload and a user message and returns an AI workflow result")
+    public ResponseEntity<AiWorkflowResponse> orchestrate(
+            @Valid @ModelAttribute AiWorkflowRequest request) throws IOException {
+        return ResponseEntity.ok(aiWorkflowService.orchestrate(request));
+    }
+
+    @PostMapping(value = "/pdf/edit", consumes = MediaType.APPLICATION_JSON_VALUE)
+    @Operation(
+            summary = "Generate a PDF edit plan",
+            description =
+                    "Sends a user message to the PDF edit agent which returns a structured plan"
+                            + " of tool operations to perform")
+    public ResponseEntity<String> pdfEdit(@RequestBody String requestBody) throws IOException {
+        validateJson(requestBody);
+        String response = aiEngineClient.post("/api/v1/pdf/edit", requestBody);
+        return ResponseEntity.ok().contentType(MediaType.APPLICATION_JSON).body(response);
+    }
+
+    private void validateJson(String body) {
+        try {
+            objectMapper.readValue(body, JsonNode.class);
+        } catch (JacksonException e) {
+            throw new ResponseStatusException(
+                    HttpStatus.BAD_REQUEST, "Request body is not valid JSON");
+        }
+    }
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiPdfContentType.java

@@ -0,0 +1,57 @@
+package stirling.software.proprietary.model.api.ai;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonValue;
+
+/**
+ * Types of content that can be extracted from a PDF and sent to the AI.
+ *
+ * <p>Values MUST match {@code PdfContentType} in {@code engine/src/stirling/contracts/common.py}.
+ */
+public enum AiPdfContentType {
+    // Document-level structured data
+    PAGE_LAYOUT("page_layout"),
+    DOCUMENT_METADATA("document_metadata"),
+    ENCRYPTION_INFO("encryption_info"),
+    BOOKMARKS("bookmarks"),
+    LAYERS("layers"),
+    EMBEDDED_FILES("embedded_files"),
+    JAVASCRIPT("javascript"),
+    LINKS("links"),
+    IMAGE_INFO("image_info"),
+    FONTS("fonts"),
+
+    // Text and content
+    PAGE_TEXT("page_text"),
+    FULL_TEXT("full_text"),
+    FORM_FIELDS("form_fields"),
+    ANNOTATIONS("annotations"),
+    SIGNATURES("signatures"),
+    STRUCTURE_TREE("structure_tree"),
+    XMP_METADATA("xmp_metadata"),
+
+    // Heavy content
+    COMPLIANCE("compliance"),
+    IMAGES("images");
+
+    private final String value;
+
+    AiPdfContentType(String value) {
+        this.value = value;
+    }
+
+    @JsonValue
+    public String getValue() {
+        return value;
+    }
+
+    @JsonCreator
+    public static AiPdfContentType fromValue(String value) {
+        for (AiPdfContentType type : values()) {
+            if (type.value.equals(value)) {
+                return type;
+            }
+        }
+        throw new IllegalArgumentException("Unknown PDF content type: " + value);
+    }
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowFileInput.java

@@ -0,0 +1,22 @@
+package stirling.software.proprietary.model.api.ai;
+
+import org.springframework.http.MediaType;
+import org.springframework.web.multipart.MultipartFile;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import jakarta.validation.constraints.NotNull;
+
+import lombok.Data;
+
+@Data
+@Schema(description = "A single PDF file input")
+public class AiWorkflowFileInput {
+
+    @NotNull
+    @Schema(
+            description = "The input PDF file",
+            contentMediaType = MediaType.APPLICATION_PDF_VALUE,
+            format = "binary")
+    private MultipartFile fileInput;
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowFileRequest.java

@@ -0,0 +1,22 @@
+package stirling.software.proprietary.model.api.ai;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import lombok.Data;
+
+@Data
+@Schema(description = "Per-file content extraction request from the AI engine")
+public class AiWorkflowFileRequest {
+
+    @Schema(description = "Original filename of the requested file", example = "contract.pdf")
+    private String fileName;
+
+    @Schema(description = "Specific 1-based page numbers to extract from this file")
+    private List<Integer> pageNumbers = new ArrayList<>();
+
+    @Schema(description = "Content types to extract from this file")
+    private List<AiPdfContentType> contentTypes = new ArrayList<>();
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowOutcome.java

@@ -0,0 +1,43 @@
+package stirling.software.proprietary.model.api.ai;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonValue;
+
+/**
+ * Discriminator values for AI workflow responses.
+ *
+ * <p>Values MUST match {@code WorkflowOutcome} in {@code engine/src/stirling/contracts/common.py}.
+ */
+public enum AiWorkflowOutcome {
+    ANSWER("answer"),
+    NOT_FOUND("not_found"),
+    NEED_CONTENT("need_content"),
+    PLAN("plan"),
+    NEED_CLARIFICATION("need_clarification"),
+    CANNOT_DO("cannot_do"),
+    TOOL_CALL("tool_call"),
+    COMPLETED("completed"),
+    UNSUPPORTED_CAPABILITY("unsupported_capability"),
+    CANNOT_CONTINUE("cannot_continue");
+
+    private final String value;
+
+    AiWorkflowOutcome(String value) {
+        this.value = value;
+    }
+
+    @JsonValue
+    public String getValue() {
+        return value;
+    }
+
+    @JsonCreator
+    public static AiWorkflowOutcome fromValue(String value) {
+        for (AiWorkflowOutcome outcome : values()) {
+            if (outcome.value.equals(value)) {
+                return outcome;
+            }
+        }
+        throw new IllegalArgumentException("Unknown AI workflow outcome: " + value);
+    }
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowRequest.java

@@ -0,0 +1,23 @@
+package stirling.software.proprietary.model.api.ai;
+
+import java.util.List;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+
+import lombok.Data;
+
+@Data
+@Schema(description = "Run an AI workflow against one or more PDF files")
+public class AiWorkflowRequest {
+
+    @NotNull
+    @Schema(description = "The input PDF files")
+    private List<AiWorkflowFileInput> fileInputs;
+
+    @NotBlank
+    @Schema(description = "The user message to orchestrate", example = "Summarise these documents")
+    private String userMessage;
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowResponse.java

@@ -0,0 +1,58 @@
+package stirling.software.proprietary.model.api.ai;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import lombok.Data;
+
+@Data
+@Schema(description = "Structured AI workflow result")
+public class AiWorkflowResponse {
+
+    @Schema(description = "Workflow outcome")
+    private AiWorkflowOutcome outcome;
+
+    @Schema(description = "Answer returned by the AI workflow when applicable")
+    private String answer;
+
+    @Schema(description = "Summary returned by the AI workflow when applicable")
+    private String summary;
+
+    @Schema(description = "Rationale returned by the AI workflow when applicable")
+    private String rationale;
+
+    @Schema(description = "Reason when the AI workflow cannot proceed")
+    private String reason;
+
+    @Schema(description = "Clarification question for the user when more input is required")
+    private String question;
+
+    @Schema(
+            description =
+                    "Unsupported capability identifier when the workflow cannot route the request")
+    private String capability;
+
+    @Schema(description = "Message returned for unsupported capability outcomes")
+    private String message;
+
+    @Schema(description = "Supporting evidence snippets from extracted PDF text")
+    private List<AiWorkflowTextSelection> evidence = new ArrayList<>();
+
+    @Schema(description = "Structured tool steps when the workflow returns a plan")
+    private List<Map<String, Object>> steps = new ArrayList<>();
+
+    @Schema(description = "Per-file text extraction requests from the AI engine")
+    private List<AiWorkflowFileRequest> files = new ArrayList<>();
+
+    @Schema(description = "Maximum number of pages the AI engine wants text extracted from")
+    private Integer maxPages;
+
+    @Schema(description = "Maximum number of characters the AI engine wants extracted")
+    private Integer maxCharacters;
+
+    @Schema(description = "AI engine capability to resume with on the next turn")
+    private String resumeWith;
+}

app/proprietary/src/main/java/stirling/software/proprietary/model/api/ai/AiWorkflowTextSelection.java

@@ -0,0 +1,16 @@
+package stirling.software.proprietary.model.api.ai;
+
+import io.swagger.v3.oas.annotations.media.Schema;
+
+import lombok.Data;
+
+@Data
+@Schema(description = "Page-scoped extracted text selection")
+public class AiWorkflowTextSelection {
+
+    @Schema(description = "1-based page number", example = "2")
+    private Integer pageNumber;
+
+    @Schema(description = "Extracted text or evidence snippet")
+    private String text;
+}

app/proprietary/src/main/java/stirling/software/proprietary/service/AiEngineClient.java

@@ -0,0 +1,108 @@
+package stirling.software.proprietary.service;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.time.Duration;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Service;
+import org.springframework.web.server.ResponseStatusException;
+
+import lombok.extern.slf4j.Slf4j;
+
+import stirling.software.common.model.ApplicationProperties;
+
+@Slf4j
+@Service
+public class AiEngineClient {
+
+    private final ApplicationProperties applicationProperties;
+    private final HttpClient httpClient;
+
+    public AiEngineClient(ApplicationProperties applicationProperties) {
+        this.applicationProperties = applicationProperties;
+        this.httpClient =
+                HttpClient.newBuilder()
+                        .connectTimeout(
+                                Duration.ofSeconds(
+                                        applicationProperties.getAiEngine().getTimeoutSeconds()))
+                        .build();
+    }
+
+    public String post(String path, String jsonBody) throws IOException {
+        ApplicationProperties.AiEngine config = applicationProperties.getAiEngine();
+        if (!config.isEnabled()) {
+            throw new ResponseStatusException(
+                    HttpStatus.SERVICE_UNAVAILABLE, "AI engine is not enabled");
+        }
+
+        String url = config.getUrl().stripTrailing() + path;
+        log.debug("Proxying AI engine request to {}", url);
+
+        HttpRequest request =
+                HttpRequest.newBuilder()
+                        .uri(URI.create(url))
+                        .header("Content-Type", "application/json")
+                        .header("Accept", "application/json")
+                        .timeout(Duration.ofSeconds(config.getTimeoutSeconds()))
+                        .POST(HttpRequest.BodyPublishers.ofString(jsonBody))
+                        .build();
+
+        HttpResponse<String> response = sendRequest(request);
+
+        log.debug("AI engine responded with status {}", response.statusCode());
+        checkResponseStatus(response);
+        return response.body();
+    }
+
+    public String get(String path) throws IOException {
+        ApplicationProperties.AiEngine config = applicationProperties.getAiEngine();
+        if (!config.isEnabled()) {
+            throw new ResponseStatusException(
+                    HttpStatus.SERVICE_UNAVAILABLE, "AI engine is not enabled");
+        }
+
+        String url = config.getUrl().stripTrailing() + path;
+        log.debug("Proxying AI engine GET request to {}", url);
+
+        HttpRequest request =
+                HttpRequest.newBuilder()
+                        .uri(URI.create(url))
+                        .header("Accept", "application/json")
+                        .timeout(Duration.ofSeconds(config.getTimeoutSeconds()))
+                        .GET()
+                        .build();
+
+        HttpResponse<String> response = sendRequest(request);
+
+        log.debug("AI engine responded with status {}", response.statusCode());
+        checkResponseStatus(response);
+        return response.body();
+    }
+
+    private HttpResponse<String> sendRequest(HttpRequest request) throws IOException {
+        try {
+            return httpClient.send(request, HttpResponse.BodyHandlers.ofString());
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+            throw new ResponseStatusException(
+                    HttpStatus.SERVICE_UNAVAILABLE, "AI engine request was interrupted");
+        }
+    }
+
+    private void checkResponseStatus(HttpResponse<String> response) {
+        int status = response.statusCode();
+        if (status >= 500) {
+            throw new ResponseStatusException(
+                    HttpStatus.BAD_GATEWAY, "AI engine returned error: " + status);
+        }
+        if (status >= 400) {
+            throw new ResponseStatusException(
+                    HttpStatus.valueOf(status),
+                    "AI engine returned client error: " + response.body());
+        }
+    }
+}

app/proprietary/src/main/java/stirling/software/proprietary/service/AiWorkflowService.java

@@ -0,0 +1,181 @@
+package stirling.software.proprietary.service;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.springframework.stereotype.Service;
+import org.springframework.web.multipart.MultipartFile;
+
+import lombok.Data;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+import stirling.software.common.service.CustomPDFDocumentFactory;
+import stirling.software.common.util.ExceptionUtils;
+import stirling.software.proprietary.model.api.ai.AiWorkflowFileInput;
+import stirling.software.proprietary.model.api.ai.AiWorkflowFileRequest;
+import stirling.software.proprietary.model.api.ai.AiWorkflowOutcome;
+import stirling.software.proprietary.model.api.ai.AiWorkflowRequest;
+import stirling.software.proprietary.model.api.ai.AiWorkflowResponse;
+import stirling.software.proprietary.service.PdfContentExtractor.LoadedFile;
+import stirling.software.proprietary.service.PdfContentExtractor.PdfContentResult;
+import stirling.software.proprietary.service.PdfContentExtractor.WorkflowArtifact;
+
+import tools.jackson.databind.ObjectMapper;
+
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class AiWorkflowService {
+
+    private final CustomPDFDocumentFactory pdfDocumentFactory;
+    private final AiEngineClient aiEngineClient;
+    private final PdfContentExtractor pdfContentExtractor;
+    private final ObjectMapper objectMapper;
+
+    private sealed interface WorkflowState {
+        record Pending(WorkflowTurnRequest request) implements WorkflowState {}
+
+        record Terminal(AiWorkflowResponse response) implements WorkflowState {}
+    }
+
+    public AiWorkflowResponse orchestrate(AiWorkflowRequest request) throws IOException {
+        validateRequest(request);
+
+        Map<String, MultipartFile> filesByName = new LinkedHashMap<>();
+        for (AiWorkflowFileInput fileInput : request.getFileInputs()) {
+            filesByName.put(
+                    fileInput.getFileInput().getOriginalFilename(), fileInput.getFileInput());
+        }
+
+        WorkflowTurnRequest initialRequest = new WorkflowTurnRequest();
+        initialRequest.setUserMessage(request.getUserMessage().trim());
+        initialRequest.setFileNames(new ArrayList<>(filesByName.keySet()));
+
+        WorkflowState state = new WorkflowState.Pending(initialRequest);
+        while (state instanceof WorkflowState.Pending pending) {
+            state = advance(pending.request(), filesByName);
+        }
+        return ((WorkflowState.Terminal) state).response();
+    }
+
+    private WorkflowState advance(
+            WorkflowTurnRequest request, Map<String, MultipartFile> filesByName)
+            throws IOException {
+        AiWorkflowResponse response = invokeOrchestrator(request);
+        return switch (response.getOutcome()) {
+            case NEED_CONTENT -> onNeedContent(response, filesByName, request);
+            case ANSWER,
+                    NOT_FOUND,
+                    PLAN,
+                    NEED_CLARIFICATION,
+                    CANNOT_DO,
+                    TOOL_CALL,
+                    COMPLETED,
+                    UNSUPPORTED_CAPABILITY,
+                    CANNOT_CONTINUE ->
+                    new WorkflowState.Terminal(response);
+        };
+    }
+
+    private WorkflowState onNeedContent(
+            AiWorkflowResponse response,
+            Map<String, MultipartFile> filesByName,
+            WorkflowTurnRequest request)
+            throws IOException {
+        if (!request.getArtifacts().isEmpty()) {
+            return new WorkflowState.Terminal(
+                    cannotContinue("AI engine requested content extraction more than once."));
+        }
+
+        List<AiWorkflowFileRequest> requestedFiles = response.getFiles();
+
+        // Validate requested file names before loading anything
+        if (requestedFiles != null && !requestedFiles.isEmpty()) {
+            for (AiWorkflowFileRequest fileReq : requestedFiles) {
+                if (!filesByName.containsKey(fileReq.getFileName())) {
+                    return new WorkflowState.Terminal(
+                            cannotContinue(
+                                    "AI engine requested unknown file: " + fileReq.getFileName()));
+                }
+            }
+        }
+
+        List<String> fileNamesToLoad =
+                (requestedFiles == null || requestedFiles.isEmpty())
+                        ? new ArrayList<>(filesByName.keySet())
+                        : requestedFiles.stream().map(AiWorkflowFileRequest::getFileName).toList();
+
+        Map<String, AiWorkflowFileRequest> requestedByName =
+                requestedFiles == null || requestedFiles.isEmpty()
+                        ? Map.of()
+                        : requestedFiles.stream()
+                                .collect(
+                                        Collectors.toMap(
+                                                AiWorkflowFileRequest::getFileName, r -> r));
+
+        List<LoadedFile> loadedFiles = new ArrayList<>();
+        try {
+            for (String fileName : fileNamesToLoad) {
+                PDDocument doc = pdfDocumentFactory.load(filesByName.get(fileName), true);
+                loadedFiles.add(new LoadedFile(fileName, doc));
+            }
+
+            List<PdfContentResult> contentResults =
+                    pdfContentExtractor.extractContent(
+                            loadedFiles,
+                            requestedByName,
+                            response.getMaxPages(),
+                            response.getMaxCharacters());
+
+            WorkflowTurnRequest nextRequest = new WorkflowTurnRequest();
+            nextRequest.setUserMessage(request.getUserMessage());
+            nextRequest.setFileNames(request.getFileNames());
+            nextRequest.setArtifacts(pdfContentExtractor.buildArtifacts(contentResults));
+            nextRequest.setResumeWith(response.getResumeWith());
+            return new WorkflowState.Pending(nextRequest);
+        } finally {
+            for (LoadedFile lf : loadedFiles) {
+                try {
+                    lf.document().close();
+                } catch (IOException e) {
+                    log.warn("Failed to close PDF document: {}", lf.fileName(), e);
+                }
+            }
+        }
+    }
+
+    private void validateRequest(AiWorkflowRequest request) {
+        for (AiWorkflowFileInput fileInput : request.getFileInputs()) {
+            if (fileInput.getFileInput().isEmpty()) {
+                throw ExceptionUtils.createFileNullOrEmptyException();
+            }
+        }
+    }
+
+    private AiWorkflowResponse cannotContinue(String reason) {
+        AiWorkflowResponse response = new AiWorkflowResponse();
+        response.setOutcome(AiWorkflowOutcome.CANNOT_CONTINUE);
+        response.setReason(reason);
+        return response;
+    }
+
+    private AiWorkflowResponse invokeOrchestrator(WorkflowTurnRequest request) throws IOException {
+        String requestBody = objectMapper.writeValueAsString(request);
+        String responseBody = aiEngineClient.post("/api/v1/orchestrator", requestBody);
+        return objectMapper.readValue(responseBody, AiWorkflowResponse.class);
+    }
+
+    @Data
+    private static class WorkflowTurnRequest {
+        private String userMessage;
+        private List<String> fileNames = new ArrayList<>();
+        private List<WorkflowArtifact> artifacts = new ArrayList<>();
+        private String resumeWith;
+    }
+}

app/proprietary/src/main/java/stirling/software/proprietary/service/PdfContentExtractor.java

@@ -0,0 +1,279 @@
+package stirling.software.proprietary.service;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.apache.pdfbox.pdmodel.PDDocument;
+import org.apache.pdfbox.text.PDFTextStripper;
+import org.springframework.stereotype.Service;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.fasterxml.jackson.annotation.JsonValue;
+
+import lombok.Data;
+import lombok.extern.slf4j.Slf4j;
+
+import stirling.software.common.util.ExceptionUtils;
+import stirling.software.proprietary.model.api.ai.AiPdfContentType;
+import stirling.software.proprietary.model.api.ai.AiWorkflowFileRequest;
+import stirling.software.proprietary.model.api.ai.AiWorkflowTextSelection;
+
+@Slf4j
+@Service
+public class PdfContentExtractor {
+
+    private static final int MAX_CHARACTERS_PER_PAGE = 4_000;
+
+    record LoadedFile(String fileName, PDDocument document) {}
+
+    /**
+     * Extracts content from the loaded files according to the requested content types and budget
+     * constraints.
+     */
+    List<PdfContentResult> extractContent(
+            List<LoadedFile> loadedFiles,
+            Map<String, AiWorkflowFileRequest> requestedByName,
+            int maxPages,
+            int maxCharacters)
+            throws IOException {
+        List<PdfContentResult> contentResults = new ArrayList<>();
+        int remainingPages = maxPages;
+        int remainingCharacters = maxCharacters;
+
+        for (LoadedFile lf : loadedFiles) {
+            if (remainingPages <= 0 || remainingCharacters <= 0) break;
+            AiWorkflowFileRequest fileReq = requestedByName.get(lf.fileName());
+            List<AiPdfContentType> contentTypes =
+                    fileReq != null && !fileReq.getContentTypes().isEmpty()
+                            ? fileReq.getContentTypes()
+                            : List.of(AiPdfContentType.PAGE_TEXT);
+
+            for (AiPdfContentType contentType : contentTypes) {
+                Optional<PdfContentResult> result =
+                        dispatchContentType(
+                                contentType, lf, fileReq, remainingPages, remainingCharacters);
+                if (result.isPresent()) {
+                    PdfContentResult content = result.get();
+                    contentResults.add(content);
+                    remainingPages -= content.pagesConsumed();
+                    remainingCharacters -= content.charactersConsumed();
+                }
+            }
+        }
+        return contentResults;
+    }
+
+    /** Groups content results by artifact kind and builds the corresponding workflow artifacts. */
+    List<WorkflowArtifact> buildArtifacts(List<PdfContentResult> results) {
+        List<WorkflowArtifact> artifacts = new ArrayList<>();
+        Map<ArtifactKind, List<PdfContentResult>> byKind =
+                results.stream().collect(Collectors.groupingBy(PdfContentResult::getArtifactKind));
+        for (var entry : byKind.entrySet()) {
+            artifacts.add(buildArtifact(entry.getKey(), entry.getValue()));
+        }
+        return artifacts;
+    }
+
+    private Optional<PdfContentResult> dispatchContentType(
+            AiPdfContentType contentType,
+            LoadedFile lf,
+            AiWorkflowFileRequest fileReq,
+            int remainingPages,
+            int remainingCharacters)
+            throws IOException {
+        return switch (contentType) {
+            case PAGE_TEXT, FULL_TEXT ->
+                    Optional.<PdfContentResult>ofNullable(
+                            extractText(lf, fileReq, remainingPages, remainingCharacters));
+            default -> {
+                log.warn(
+                        "Content type {} not yet implemented, skipping for {}",
+                        contentType,
+                        lf.fileName());
+                yield Optional.empty();
+            }
+        };
+    }
+
+    private ExtractedFileText extractText(
+            LoadedFile lf,
+            AiWorkflowFileRequest fileReq,
+            int remainingPages,
+            int remainingCharacters)
+            throws IOException {
+        List<Integer> requestedPages = fileReq != null ? fileReq.getPageNumbers() : null;
+        List<Integer> pages =
+                selectPages(lf.document().getNumberOfPages(), requestedPages, remainingPages);
+        List<AiWorkflowTextSelection> extracted =
+                extractPageText(lf.document(), pages, remainingCharacters);
+        return extracted.isEmpty() ? null : buildExtractedFileText(lf.fileName(), extracted);
+    }
+
+    private WorkflowArtifact buildArtifact(ArtifactKind kind, List<PdfContentResult> results) {
+        return switch (kind) {
+            case EXTRACTED_TEXT -> {
+                ExtractedTextArtifact artifact = new ExtractedTextArtifact();
+                artifact.setFiles(results.stream().map(ExtractedFileText.class::cast).toList());
+                yield artifact;
+            }
+        };
+    }
+
+    private List<Integer> selectPages(
+            int totalPages, List<Integer> requestedPageNumbers, int maxPages) {
+        if (totalPages <= 0) {
+            throw ExceptionUtils.createPdfNoPages();
+        }
+
+        List<Integer> pages = new ArrayList<>();
+
+        if (requestedPageNumbers == null || requestedPageNumbers.isEmpty()) {
+            for (int p = 1; p <= totalPages && pages.size() < maxPages; p++) {
+                pages.add(p);
+            }
+            return pages;
+        }
+
+        Set<Integer> deduplicatedPages = new LinkedHashSet<>(requestedPageNumbers);
+        for (Integer pageNumber : deduplicatedPages) {
+            if (pageNumber == null || pageNumber < 1 || pageNumber > totalPages) {
+                throw ExceptionUtils.createIllegalArgumentException(
+                        "error.invalidPageNumber",
+                        "Requested page number %s is outside the PDF page range.",
+                        pageNumber);
+            }
+            pages.add(pageNumber);
+            if (pages.size() >= maxPages) {
+                break;
+            }
+        }
+        return pages;
+    }
+
+    private List<AiWorkflowTextSelection> extractPageText(
+            PDDocument document, List<Integer> selectedPages, int maxCharacters)
+            throws IOException {
+        PDFTextStripper textStripper = new PDFTextStripper();
+        List<AiWorkflowTextSelection> pages = new ArrayList<>();
+        int remainingCharacters = maxCharacters;
+
+        for (Integer pageNumber : selectedPages) {
+            if (remainingCharacters <= 0) {
+                break;
+            }
+
+            textStripper.setStartPage(pageNumber);
+            textStripper.setEndPage(pageNumber);
+
+            String pageText = textStripper.getText(document).trim();
+            if (pageText.isBlank()) {
+                continue;
+            }
+
+            int allowedCharacters = Math.min(remainingCharacters, MAX_CHARACTERS_PER_PAGE);
+            String clippedText = clip(pageText, allowedCharacters);
+            if (clippedText.isBlank()) {
+                continue;
+            }
+
+            AiWorkflowTextSelection selection = new AiWorkflowTextSelection();
+            selection.setPageNumber(pageNumber);
+            selection.setText(clippedText);
+            pages.add(selection);
+            remainingCharacters -= clippedText.length();
+        }
+        return pages;
+    }
+
+    private ExtractedFileText buildExtractedFileText(
+            String fileName, List<AiWorkflowTextSelection> pages) {
+        ExtractedFileText fileText = new ExtractedFileText();
+        fileText.setFileName(fileName);
+        fileText.setPages(pages);
+        return fileText;
+    }
+
+    private String clip(String text, int maxLength) {
+        if (text.length() <= maxLength) {
+            return text;
+        }
+        // Avoid splitting a surrogate pair at the boundary
+        int end = maxLength;
+        if (Character.isHighSurrogate(text.charAt(end - 1))) {
+            end--;
+        }
+        return text.substring(0, end);
+    }
+
+    // --- Types shared with AiWorkflowService (package-private) ---
+
+    interface PdfContentResult {
+        @JsonIgnore
+        ArtifactKind getArtifactKind();
+
+        @JsonIgnore
+        default int pagesConsumed() {
+            return 0;
+        }
+
+        @JsonIgnore
+        default int charactersConsumed() {
+            return 0;
+        }
+    }
+
+    /**
+     * Values MUST match {@code ArtifactKind} in {@code engine/src/stirling/contracts/common.py}.
+     */
+    enum ArtifactKind {
+        EXTRACTED_TEXT("extracted_text");
+
+        private final String value;
+
+        ArtifactKind(String value) {
+            this.value = value;
+        }
+
+        @JsonValue
+        public String getValue() {
+            return value;
+        }
+    }
+
+    interface WorkflowArtifact {
+        ArtifactKind getKind();
+    }
+
+    @Data
+    static class ExtractedFileText implements PdfContentResult {
+        private String fileName;
+        private List<AiWorkflowTextSelection> pages = new ArrayList<>();
+
+        @Override
+        public ArtifactKind getArtifactKind() {
+            return ArtifactKind.EXTRACTED_TEXT;
+        }
+
+        @Override
+        public int pagesConsumed() {
+            return pages.size();
+        }
+
+        @Override
+        public int charactersConsumed() {
+            return pages.stream().mapToInt(p -> p.getText().length()).sum();
+        }
+    }
+
+    @Data
+    static final class ExtractedTextArtifact implements WorkflowArtifact {
+        private final ArtifactKind kind = ArtifactKind.EXTRACTED_TEXT;
+        private List<ExtractedFileText> files = new ArrayList<>();
+    }
+}

engine/pyproject.toml

@@ -42,9 +42,8 @@ select = [
     "W",
     "RUF100",
     "UP",
-]
+    "PYI",    # flake8-pyi: flags deprecated typing constructs
-ignore = [
+    "FA",     # flake8-future-annotations: flags missing future annotations imports
-    "E501", # Temporarily disable line length limit until codebase conformat
 ]
 
 [tool.pyright]
@@ -55,6 +54,7 @@ reportUnnecessaryCast = "warning"
 reportUnnecessaryTypeIgnoreComment = "warning"
 reportUnusedImport = "warning"
 reportUnknownParameterType = "warning"
+reportDeprecated = "warning"
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]

engine/src/stirling/agents/orchestrator.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from typing import assert_never
 
 from pydantic_ai import Agent
 from pydantic_ai.output import ToolOutput
@@ -12,12 +13,14 @@ from stirling.agents.user_spec import UserSpecAgent
 from stirling.contracts import (
     AgentDraftRequest,
     AgentDraftWorkflowResponse,
+    ExtractedTextArtifact,
     OrchestratorRequest,
     OrchestratorResponse,
     PdfEditRequest,
     PdfEditResponse,
     PdfQuestionRequest,
     PdfQuestionResponse,
+    SupportedCapability,
     UnsupportedCapabilityResponse,
 )
 from stirling.services import AppRuntime
@@ -61,7 +64,7 @@ class OrchestratorAgent:
                 "You are the top-level orchestrator. "
                 "Choose exactly one output function that best handles the request. "
                 "Use delegate_pdf_edit for requested PDF modifications. "
-                "Use delegate_pdf_question for questions about the contents of a PDF. "
+                "Use delegate_pdf_question for questions about PDF contents. "
                 "Use delegate_user_spec for requests to create or define an agent spec. "
                 "Use unsupported_capability only when none of the other outputs fit."
             ),
@@ -69,27 +72,56 @@ class OrchestratorAgent:
         )
 
     async def handle(self, request: OrchestratorRequest) -> OrchestratorResponse:
+        if request.resume_with is not None:
+            return await self._resume(request, request.resume_with)
         result = await self.agent.run(
-            request.user_message,
+            self._build_prompt(request),
             deps=OrchestratorDeps(runtime=self.runtime, request=request),
         )
         return result.output
 
+    async def _resume(self, request: OrchestratorRequest, capability: SupportedCapability) -> OrchestratorResponse:
+        """Fast-path to get back to the correct endpoint without having to call AI."""
+        match capability:
+            case SupportedCapability.PDF_QUESTION:
+                return await self._run_pdf_question(request)
+            case SupportedCapability.PDF_EDIT:
+                return await self._run_pdf_edit(request)
+            case SupportedCapability.AGENT_DRAFT:
+                return await self._run_agent_draft(request)
+            case (
+                SupportedCapability.ORCHESTRATE
+                | SupportedCapability.AGENT_REVISE
+                | SupportedCapability.AGENT_NEXT_ACTION
+            ):
+                raise ValueError(f"Cannot resume orchestrator with capability: {capability}")
+            case _ as unreachable:
+                assert_never(unreachable)
+
     async def delegate_pdf_edit(self, ctx: RunContext[OrchestratorDeps]) -> PdfEditResponse:
-        request = ctx.deps.request
+        return await self._run_pdf_edit(ctx.deps.request)
-        return await PdfEditAgent(ctx.deps.runtime).handle(
+
-            PdfEditRequest(user_message=request.user_message, conversation_id=request.conversation_id)
+    async def _run_pdf_edit(self, request: OrchestratorRequest) -> PdfEditResponse:
-        )
+        return await PdfEditAgent(self.runtime).handle(PdfEditRequest(user_message=request.user_message))
 
     async def delegate_pdf_question(self, ctx: RunContext[OrchestratorDeps]) -> PdfQuestionResponse:
-        request = ctx.deps.request
+        return await self._run_pdf_question(ctx.deps.request)
-        return await PdfQuestionAgent(ctx.deps.runtime).handle(
+
-            PdfQuestionRequest(question=request.user_message, conversation_id=request.conversation_id)
+    async def _run_pdf_question(self, request: OrchestratorRequest) -> PdfQuestionResponse:
+        extracted_text = self._get_extracted_text_artifact(request)
+        return await PdfQuestionAgent(self.runtime).handle(
+            PdfQuestionRequest(
+                question=request.user_message,
+                file_names=request.file_names,
+                page_text=extracted_text.files if extracted_text is not None else [],
+            )
         )
 
     async def delegate_user_spec(self, ctx: RunContext[OrchestratorDeps]) -> AgentDraftWorkflowResponse:
-        request = ctx.deps.request
+        return await self._run_agent_draft(ctx.deps.request)
-        return await UserSpecAgent(ctx.deps.runtime).draft(AgentDraftRequest(user_message=request.user_message))
+
+    async def _run_agent_draft(self, request: OrchestratorRequest) -> AgentDraftWorkflowResponse:
+        return await UserSpecAgent(self.runtime).draft(AgentDraftRequest(user_message=request.user_message))
 
     async def unsupported_capability(
         self,
@@ -98,3 +130,28 @@ class OrchestratorAgent:
         message: str,
     ) -> UnsupportedCapabilityResponse:
         return UnsupportedCapabilityResponse(capability=capability, message=message)
+
+    def _get_extracted_text_artifact(self, request: OrchestratorRequest) -> ExtractedTextArtifact | None:
+        for artifact in request.artifacts:
+            if isinstance(artifact, ExtractedTextArtifact):
+                return artifact
+        return None
+
+    def _build_prompt(self, request: OrchestratorRequest) -> str:
+        artifact_summary = self._describe_artifacts(request)
+        file_names = ", ".join(request.file_names) if request.file_names else "Unknown files"
+        return f"User message: {request.user_message}\nFiles: {file_names}\nAvailable artifacts:\n{artifact_summary}"
+
+    def _describe_artifacts(self, request: OrchestratorRequest) -> str:
+        if not request.artifacts:
+            return "- none"
+
+        descriptions: list[str] = []
+        for artifact in request.artifacts:
+            if isinstance(artifact, ExtractedTextArtifact):
+                total_pages = sum(len(f.pages) for f in artifact.files)
+                file_names = [f.file_name for f in artifact.files]
+                descriptions.append(f"- extracted_text: {total_pages} pages from {file_names}")
+                continue
+            descriptions.append("- unknown artifact")
+        return "\n".join(descriptions)

engine/src/stirling/agents/pdf_questions.py

@@ -4,8 +4,11 @@ from pydantic_ai import Agent
 from pydantic_ai.output import NativeOutput
 
 from stirling.contracts import (
+    ExtractedFileText,
+    NeedContentFileRequest,
+    PdfContentType,
     PdfQuestionAnswerResponse,
-    PdfQuestionNeedTextResponse,
+    PdfQuestionNeedContentResponse,
     PdfQuestionNotFoundResponse,
     PdfQuestionRequest,
     PdfQuestionResponse,
@@ -14,6 +17,9 @@ from stirling.services import AppRuntime
 
 
 class PdfQuestionAgent:
+    DEFAULT_MAX_PAGES = 12
+    DEFAULT_MAX_CHARACTERS = 24_000
+
     def __init__(self, runtime: AppRuntime) -> None:
         self.runtime = runtime
         self.agent = Agent(
@@ -25,18 +31,27 @@ class PdfQuestionAgent:
                 ]
             ),
             system_prompt=(
-                "Answer questions about a PDF using only the extracted text provided in the prompt. "
+                "Answer questions about PDFs using only the extracted page text provided in the prompt. "
                 "Do not guess or use outside knowledge. "
                 "If the answer is not supported by the provided text, return not_found. "
-                "When answering, include a short list of evidence snippets copied from the provided text."
+                "When answering, include a short list of evidence snippets with their page numbers."
             ),
             model_settings=runtime.smart_model_settings,
         )
 
     async def handle(self, request: PdfQuestionRequest) -> PdfQuestionResponse:
-        if not request.extracted_text.strip():
+        if not self._has_page_text(request.page_text):
-            return PdfQuestionNeedTextResponse(
+            return PdfQuestionNeedContentResponse(
-                reason="No extracted PDF text was provided, so the question cannot be answered yet."
+                reason="No extracted PDF page text was provided, so the question cannot be answered yet.",
+                files=[
+                    NeedContentFileRequest(
+                        file_name=file_name,
+                        content_types=[PdfContentType.PAGE_TEXT],
+                    )
+                    for file_name in request.file_names
+                ],
+                max_pages=self.DEFAULT_MAX_PAGES,
+                max_characters=self.DEFAULT_MAX_CHARACTERS,
             )
         return await self._run_answer_agent(request)
 
@@ -45,5 +60,14 @@ class PdfQuestionAgent:
         return result.output
 
     def _build_prompt(self, request: PdfQuestionRequest) -> str:
-        file_name = request.file_name or "Unknown file"
+        file_names = ", ".join(request.file_names) if request.file_names else "Unknown files"
-        return f"File: {file_name}\nQuestion: {request.question}\nExtracted text:\n{request.extracted_text}"
+        sections = [
+            f"[File: {file_text.file_name}, Page {selection.page_number or '?'}]\n{selection.text}"
+            for file_text in request.page_text
+            for selection in file_text.pages
+        ]
+        pages = "\n\n".join(sections)
+        return f"Files: {file_names}\nQuestion: {request.question}\nExtracted page text:\n{pages}"
+
+    def _has_page_text(self, page_text: list[ExtractedFileText]) -> bool:
+        return any(selection.text.strip() for file_text in page_text for selection in file_text.pages)

engine/src/stirling/contracts/__init__.py

@@ -8,7 +8,17 @@ from .agent_drafts import (
     AgentRevisionWorkflowResponse,
 )
 from .agent_specs import AgentSpec, AgentSpecStep, AiToolAgentStep
-from .common import ConversationMessage, PdfTextSelection, ToolOperationStep
+from .common import (
+    ArtifactKind,
+    ConversationMessage,
+    ExtractedFileText,
+    PdfContentType,
+    PdfTextSelection,
+    StepKind,
+    SupportedCapability,
+    ToolOperationStep,
+    WorkflowOutcome,
+)
 from .execution import (
     AgentExecutionRequest,
     CannotContinueExecutionAction,
@@ -19,7 +29,13 @@ from .execution import (
     ToolCallExecutionAction,
 )
 from .health import HealthResponse
-from .orchestrator import OrchestratorRequest, OrchestratorResponse, SupportedCapability, UnsupportedCapabilityResponse
+from .orchestrator import (
+    ExtractedTextArtifact,
+    OrchestratorRequest,
+    OrchestratorResponse,
+    UnsupportedCapabilityResponse,
+    WorkflowArtifact,
+)
 from .pdf_edit import (
     EditCannotDoResponse,
     EditClarificationRequest,
@@ -28,14 +44,16 @@ from .pdf_edit import (
     PdfEditResponse,
 )
 from .pdf_questions import (
+    NeedContentFileRequest,
     PdfQuestionAnswerResponse,
-    PdfQuestionNeedTextResponse,
+    PdfQuestionNeedContentResponse,
     PdfQuestionNotFoundResponse,
     PdfQuestionRequest,
     PdfQuestionResponse,
 )
 
 __all__ = [
+    "ArtifactKind",
     "AgentDraft",
     "AgentDraftRequest",
     "AgentDraftResponse",
@@ -49,6 +67,7 @@ __all__ = [
     "AiToolAgentStep",
     "CannotContinueExecutionAction",
     "ConversationMessage",
+    "ExtractedFileText",
     "CompletedExecutionAction",
     "EditCannotDoResponse",
     "EditClarificationRequest",
@@ -56,19 +75,25 @@ __all__ = [
     "ExecutionContext",
     "ExecutionStepResult",
     "HealthResponse",
+    "NeedContentFileRequest",
     "NextExecutionAction",
+    "ExtractedTextArtifact",
     "OrchestratorRequest",
     "OrchestratorResponse",
     "PdfEditRequest",
     "PdfEditResponse",
     "PdfQuestionAnswerResponse",
     "PdfQuestionNotFoundResponse",
-    "PdfQuestionNeedTextResponse",
+    "PdfContentType",
+    "PdfQuestionNeedContentResponse",
     "PdfQuestionRequest",
     "PdfQuestionResponse",
     "PdfTextSelection",
+    "StepKind",
     "SupportedCapability",
     "ToolOperationStep",
     "ToolCallExecutionAction",
+    "WorkflowOutcome",
     "UnsupportedCapabilityResponse",
+    "WorkflowArtifact",
 ]

engine/src/stirling/contracts/agent_drafts.py

@@ -7,12 +7,12 @@ from pydantic import Field
 from stirling.models import ApiModel
 
 from .agent_specs import AgentSpecStep
-from .common import ConversationMessage
+from .common import ConversationMessage, StepKind, WorkflowOutcome
 from .pdf_edit import EditCannotDoResponse, EditClarificationRequest
 
 
 class AgentDraftStep(ApiModel):
-    kind: Literal["tool", "ai_tool"]
+    kind: Literal[StepKind.TOOL, StepKind.AI_TOOL]
     title: str
     description: str
 
@@ -30,7 +30,7 @@ class AgentDraftRequest(ApiModel):
 
 
 class AgentDraftResponse(ApiModel):
-    outcome: Literal["draft"] = "draft"
+    outcome: Literal[WorkflowOutcome.DRAFT] = WorkflowOutcome.DRAFT
     draft: AgentDraft
 
 
@@ -41,7 +41,7 @@ class AgentRevisionRequest(ApiModel):
 
 
 class AgentRevisionResponse(ApiModel):
-    outcome: Literal["draft"] = "draft"
+    outcome: Literal[WorkflowOutcome.DRAFT] = WorkflowOutcome.DRAFT
     draft: AgentDraft
 
 

engine/src/stirling/contracts/agent_specs.py

@@ -6,11 +6,11 @@ from pydantic import Field
 
 from stirling.models import ApiModel, OperationId
 
-from .common import ToolOperationStep
+from .common import StepKind, ToolOperationStep
 
 
 class AiToolAgentStep(ApiModel):
-    kind: Literal["ai_tool"] = "ai_tool"
+    kind: Literal[StepKind.AI_TOOL] = StepKind.AI_TOOL
     title: str
     description: str
     tool: OperationId

engine/src/stirling/contracts/common.py

@@ -1,12 +1,89 @@
 from __future__ import annotations
 
+from enum import StrEnum
 from typing import Literal
 
-from pydantic import model_validator
+from pydantic import Field, model_validator
 
 from stirling.models import OPERATIONS, ApiModel, OperationId, ParamToolModel
 
 
+class PdfContentType(StrEnum):
+    """Types of content that can be extracted from a PDF and sent to the AI.
+
+    Java counterpart: AiPdfContentType.java - values must stay in sync.
+    """
+
+    # Document-level structured data
+    PAGE_LAYOUT = "page_layout"
+    DOCUMENT_METADATA = "document_metadata"
+    ENCRYPTION_INFO = "encryption_info"
+    BOOKMARKS = "bookmarks"
+    LAYERS = "layers"
+    EMBEDDED_FILES = "embedded_files"
+    JAVASCRIPT = "javascript"
+    LINKS = "links"
+    IMAGE_INFO = "image_info"
+    FONTS = "fonts"
+
+    # Text and content
+    PAGE_TEXT = "page_text"
+    FULL_TEXT = "full_text"
+    FORM_FIELDS = "form_fields"
+    ANNOTATIONS = "annotations"
+    SIGNATURES = "signatures"
+    STRUCTURE_TREE = "structure_tree"
+    XMP_METADATA = "xmp_metadata"
+
+    # Heavy content
+    COMPLIANCE = "compliance"
+    IMAGES = "images"
+
+
+class WorkflowOutcome(StrEnum):
+    """Discriminator values for all workflow response unions (outcome field).
+
+    Java counterpart: AiWorkflowOutcome.java - values must stay in sync.
+    """
+
+    ANSWER = "answer"
+    NEED_CONTENT = "need_content"
+    NOT_FOUND = "not_found"
+    PLAN = "plan"
+    NEED_CLARIFICATION = "need_clarification"
+    CANNOT_DO = "cannot_do"
+    DRAFT = "draft"
+    TOOL_CALL = "tool_call"
+    COMPLETED = "completed"
+    CANNOT_CONTINUE = "cannot_continue"
+    UNSUPPORTED_CAPABILITY = "unsupported_capability"
+
+
+class ArtifactKind(StrEnum):
+    """Discriminator values for WorkflowArtifact unions (kind field).
+
+    Java counterpart: PdfContentExtractor.ArtifactKind - values must stay in sync.
+    """
+
+    EXTRACTED_TEXT = "extracted_text"
+
+
+class StepKind(StrEnum):
+    """Discriminator values for AgentSpecStep unions (kind field)."""
+
+    TOOL = "tool"
+    AI_TOOL = "ai_tool"
+
+
+class SupportedCapability(StrEnum):
+    ORCHESTRATE = "orchestrate"
+    PDF_EDIT = "pdf_edit"
+    PDF_QUESTION = "pdf_question"
+    AGENT_DRAFT = "agent_draft"
+    AGENT_REVISE = "agent_revise"
+    AGENT_NEXT_ACTION = "agent_next_action"
+
+
 class ConversationMessage(ApiModel):
     role: str
     content: str
@@ -17,8 +94,13 @@ class PdfTextSelection(ApiModel):
     text: str
 
 
+class ExtractedFileText(ApiModel):
+    file_name: str
+    pages: list[PdfTextSelection] = Field(default_factory=list)
+
+
 class ToolOperationStep(ApiModel):
-    kind: Literal["tool"] = "tool"
+    kind: Literal[StepKind.TOOL] = StepKind.TOOL
     tool: OperationId
     parameters: ParamToolModel
 

engine/src/stirling/contracts/execution.py

@@ -7,6 +7,7 @@ from pydantic import Field
 from stirling.models import ApiModel, OperationId, ParamToolModel
 
 from .agent_specs import AgentSpec
+from .common import WorkflowOutcome
 
 
 class ExecutionStepResult(ApiModel):
@@ -31,19 +32,19 @@ class AgentExecutionRequest(ApiModel):
 
 
 class ToolCallExecutionAction(ApiModel):
-    outcome: Literal["tool_call"] = "tool_call"
+    outcome: Literal[WorkflowOutcome.TOOL_CALL] = WorkflowOutcome.TOOL_CALL
     tool: OperationId
     parameters: ParamToolModel
     rationale: str | None = None
 
 
 class CompletedExecutionAction(ApiModel):
-    outcome: Literal["completed"] = "completed"
+    outcome: Literal[WorkflowOutcome.COMPLETED] = WorkflowOutcome.COMPLETED
     summary: str
 
 
 class CannotContinueExecutionAction(ApiModel):
-    outcome: Literal["cannot_continue"] = "cannot_continue"
+    outcome: Literal[WorkflowOutcome.CANNOT_CONTINUE] = WorkflowOutcome.CANNOT_CONTINUE
     reason: str
 
 

engine/src/stirling/contracts/orchestrator.py

@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-from enum import StrEnum
 from typing import Annotated, Literal
 
 from pydantic import Field
@@ -8,27 +7,29 @@ from pydantic import Field
 from stirling.models import ApiModel
 
 from .agent_drafts import AgentDraftResponse
+from .common import ArtifactKind, ExtractedFileText, SupportedCapability, WorkflowOutcome
 from .execution import NextExecutionAction
 from .pdf_edit import PdfEditResponse
 from .pdf_questions import PdfQuestionResponse
 
 
-class SupportedCapability(StrEnum):
+class ExtractedTextArtifact(ApiModel):
-    ORCHESTRATE = "orchestrate"
+    kind: Literal[ArtifactKind.EXTRACTED_TEXT] = ArtifactKind.EXTRACTED_TEXT
-    PDF_EDIT = "pdf_edit"
+    files: list[ExtractedFileText] = Field(default_factory=list)
-    PDF_QUESTION = "pdf_question"
+
-    AGENT_DRAFT = "agent_draft"
+
-    AGENT_REVISE = "agent_revise"
+WorkflowArtifact = Annotated[ExtractedTextArtifact, Field(discriminator="kind")]
-    AGENT_NEXT_ACTION = "agent_next_action"
 
 
 class OrchestratorRequest(ApiModel):
     user_message: str
-    conversation_id: str | None = None
+    file_names: list[str]
+    artifacts: list[WorkflowArtifact] = Field(default_factory=list)
+    resume_with: SupportedCapability | None = None
 
 
 class UnsupportedCapabilityResponse(ApiModel):
-    outcome: Literal["unsupported_capability"] = "unsupported_capability"
+    outcome: Literal[WorkflowOutcome.UNSUPPORTED_CAPABILITY] = WorkflowOutcome.UNSUPPORTED_CAPABILITY
     capability: str
     message: str
 

engine/src/stirling/contracts/pdf_edit.py

@@ -6,30 +6,29 @@ from pydantic import Field
 
 from stirling.models import ApiModel
 
-from .common import ToolOperationStep
+from .common import ToolOperationStep, WorkflowOutcome
 
 
 class PdfEditRequest(ApiModel):
     user_message: str
-    conversation_id: str | None = None
     file_names: list[str] = Field(default_factory=list)
 
 
 class EditPlanResponse(ApiModel):
-    outcome: Literal["plan"] = "plan"
+    outcome: Literal[WorkflowOutcome.PLAN] = WorkflowOutcome.PLAN
     summary: str
     rationale: str | None = None
     steps: list[ToolOperationStep]
 
 
 class EditClarificationRequest(ApiModel):
-    outcome: Literal["need_clarification"] = "need_clarification"
+    outcome: Literal[WorkflowOutcome.NEED_CLARIFICATION] = WorkflowOutcome.NEED_CLARIFICATION
     question: str
     reason: str
 
 
 class EditCannotDoResponse(ApiModel):
-    outcome: Literal["cannot_do"] = "cannot_do"
+    outcome: Literal[WorkflowOutcome.CANNOT_DO] = WorkflowOutcome.CANNOT_DO
     reason: str
 
 

engine/src/stirling/contracts/pdf_questions.py

@@ -6,31 +6,42 @@ from pydantic import Field
 
 from stirling.models import ApiModel
 
+from .common import ExtractedFileText, PdfContentType, SupportedCapability, WorkflowOutcome
+
 
 class PdfQuestionRequest(ApiModel):
     question: str
-    conversation_id: str | None = None
+    page_text: list[ExtractedFileText] = Field(default_factory=list)
-    extracted_text: str = ""
+    file_names: list[str]
-    file_name: str | None = None
 
 
 class PdfQuestionAnswerResponse(ApiModel):
-    outcome: Literal["answer"] = "answer"
+    outcome: Literal[WorkflowOutcome.ANSWER] = WorkflowOutcome.ANSWER
     answer: str
-    evidence: list[str] = Field(default_factory=list)
+    evidence: list[ExtractedFileText] = Field(default_factory=list)
 
 
-class PdfQuestionNeedTextResponse(ApiModel):
+class NeedContentFileRequest(ApiModel):
-    outcome: Literal["need_text"] = "need_text"
+    file_name: str
+    page_numbers: list[int] = Field(default_factory=list)
+    content_types: list[PdfContentType]
+
+
+class PdfQuestionNeedContentResponse(ApiModel):
+    outcome: Literal[WorkflowOutcome.NEED_CONTENT] = WorkflowOutcome.NEED_CONTENT
+    resume_with: SupportedCapability = SupportedCapability.PDF_QUESTION
     reason: str
+    files: list[NeedContentFileRequest] = Field(default_factory=list)
+    max_pages: int
+    max_characters: int
 
 
 class PdfQuestionNotFoundResponse(ApiModel):
-    outcome: Literal["not_found"] = "not_found"
+    outcome: Literal[WorkflowOutcome.NOT_FOUND] = WorkflowOutcome.NOT_FOUND
     reason: str
 
 
 PdfQuestionResponse = Annotated[
-    PdfQuestionAnswerResponse | PdfQuestionNeedTextResponse | PdfQuestionNotFoundResponse,
+    PdfQuestionAnswerResponse | PdfQuestionNeedContentResponse | PdfQuestionNotFoundResponse,
     Field(discriminator="outcome"),
 ]

engine/tests/test_pdf_question_agent.py

@@ -5,10 +5,12 @@ import pytest
 from stirling.agents import PdfQuestionAgent
 from stirling.config import AppSettings
 from stirling.contracts import (
+    ExtractedFileText,
     PdfQuestionAnswerResponse,
-    PdfQuestionNeedTextResponse,
+    PdfQuestionNeedContentResponse,
     PdfQuestionNotFoundResponse,
     PdfQuestionRequest,
+    PdfTextSelection,
 )
 from stirling.services import build_runtime
 
@@ -34,13 +36,22 @@ def build_test_settings() -> AppSettings:
     )
 
 
+def invoice_page() -> ExtractedFileText:
+    return ExtractedFileText(
+        file_name="invoice.pdf",
+        pages=[PdfTextSelection(page_number=1, text="Invoice total: 120.00")],
+    )
+
+
 @pytest.mark.anyio
 async def test_pdf_question_agent_requires_extracted_text() -> None:
     agent = PdfQuestionAgent(build_runtime(build_test_settings()))
 
-    response = await agent.handle(PdfQuestionRequest(question="What is the total?", extracted_text=""))
+    response = await agent.handle(
+        PdfQuestionRequest(question="What is the total?", page_text=[], file_names=["test.pdf"])
+    )
 
-    assert isinstance(response, PdfQuestionNeedTextResponse)
+    assert isinstance(response, PdfQuestionNeedContentResponse)
 
 
 @pytest.mark.anyio
@@ -48,15 +59,15 @@ async def test_pdf_question_agent_returns_grounded_answer() -> None:
     agent = StubPdfQuestionAgent(
         PdfQuestionAnswerResponse(
             answer="The invoice total is 120.00.",
-            evidence=["Invoice total: 120.00"],
+            evidence=[invoice_page()],
         )
     )
 
     response = await agent.handle(
         PdfQuestionRequest(
             question="What is the total?",
-            extracted_text="Invoice total: 120.00",
+            page_text=[invoice_page()],
-            file_name="invoice.pdf",
+            file_names=["invoice.pdf"],
         )
     )
 
@@ -71,8 +82,13 @@ async def test_pdf_question_agent_returns_not_found_when_text_is_insufficient()
     response = await agent.handle(
         PdfQuestionRequest(
             question="What is the total?",
-            extracted_text="This page contains only a shipping address.",
+            page_text=[
-            file_name="invoice.pdf",
+                ExtractedFileText(
+                    file_name="invoice.pdf",
+                    pages=[PdfTextSelection(page_number=1, text="This page contains only a shipping address.")],
+                )
+            ],
+            file_names=["invoice.pdf"],
         )
     )
 

engine/tests/test_stirling_api.py

@@ -20,9 +20,9 @@ from stirling.contracts import (
     EditCannotDoResponse,
     OrchestratorRequest,
     PdfEditRequest,
+    PdfQuestionNeedContentResponse,
     PdfQuestionNotFoundResponse,
     PdfQuestionRequest,
-    UnsupportedCapabilityResponse,
 )
 from stirling.models.tool_models import RotateParams
 
@@ -38,8 +38,8 @@ class StubSettingsProvider:
 
 
 class StubOrchestratorAgent:
-    async def handle(self, request: OrchestratorRequest) -> UnsupportedCapabilityResponse:
+    async def handle(self, request: OrchestratorRequest) -> PdfQuestionNeedContentResponse:
-        return UnsupportedCapabilityResponse(capability="pdf_edit", message=request.user_message)
+        return PdfQuestionNeedContentResponse(reason=request.user_message, files=[], max_pages=1, max_characters=1000)
 
 
 class StubPdfEditAgent:
@@ -115,10 +115,10 @@ def test_health_route() -> None:
 
 
 def test_orchestrator_route() -> None:
-    response = client.post("/api/v1/orchestrator", json={"userMessage": "route this"})
+    response = client.post("/api/v1/orchestrator", json={"userMessage": "route this", "fileNames": ["test.pdf"]})
 
     assert response.status_code == 200
-    assert response.json()["outcome"] == "unsupported_capability"
+    assert response.json()["outcome"] == "need_content"
 
 
 def test_pdf_edit_route() -> None:
@@ -129,7 +129,14 @@ def test_pdf_edit_route() -> None:
 
 
 def test_pdf_questions_route() -> None:
-    response = client.post("/api/v1/pdf/questions", json={"question": "what is this?"})
+    response = client.post(
+        "/api/v1/pdf/questions",
+        json={
+            "question": "what is this?",
+            "fileNames": ["test.pdf"],
+            "pageText": [{"fileName": "test.pdf", "pages": [{"pageNumber": 1, "text": "Example"}]}],
+        },
+    )
 
     assert response.status_code == 200
     assert response.json()["outcome"] == "not_found"

engine/tests/test_stirling_contracts.py

@@ -9,17 +9,34 @@ from stirling.contracts import (
     AgentSpecStep,
     EditPlanResponse,
     ExecutionContext,
+    ExtractedFileText,
+    ExtractedTextArtifact,
     OrchestratorRequest,
     PdfQuestionAnswerResponse,
+    PdfTextSelection,
     ToolOperationStep,
 )
 from stirling.models.tool_models import OperationId, RotateParams
 
 
 def test_orchestrator_request_accepts_user_message() -> None:
-    request = OrchestratorRequest(user_message="Rotate the PDF")
+    request = OrchestratorRequest(
+        user_message="Rotate the PDF",
+        file_names=["test.pdf"],
+        artifacts=[
+            ExtractedTextArtifact(
+                files=[
+                    ExtractedFileText(
+                        file_name="test.pdf",
+                        pages=[PdfTextSelection(page_number=1, text="Hello")],
+                    )
+                ]
+            )
+        ],
+    )
 
     assert request.user_message == "Rotate the PDF"
+    assert len(request.artifacts) == 1
 
 
 def test_agent_execution_request_uses_typed_agent_spec() -> None: