feat: add context budget utility

src/utils/context-budget.js

@@ -1 +1,105 @@
 // Context size limit and trimming logic.
+
+/**
+ * Validates and trims input to stay within character budget.
+ *
+ * @param {{ question: string, context?: string, projectSummary?: string, taskSummary?: string, relevantFiles?: Array<{ path: string, content: string }>, logs?: string }} input
+ * @param {{ maxInputChars: number, maxFileChars: number, maxFiles: number, maxLogChars: number }} config
+ * @returns {{ ok: true, input: object, warnings: string[] } | { ok: false, error: string, warnings: string[], input: null }}
+ */
+export function checkContextBudget(input, config) {
+  if (!input || typeof input.question !== 'string' || input.question.length === 0) {
+    throw new Error('Validation error: question is required.');
+  }
+
+  const warnings = [];
+  const files = input.relevantFiles ? [...input.relevantFiles] : [];
+  let logs = input.logs ?? '';
+  let context = input.context ?? '';
+  let projectSummary = input.projectSummary ?? '';
+  let taskSummary = input.taskSummary ?? '';
+
+  // Step 1 — Enforce hard limits (maxFiles, maxFileChars, maxLogChars)
+  if (files.length > config.maxFiles) {
+    warnings.push(`Only the first ${config.maxFiles} relevant files were kept. (maxFiles=${config.maxFiles})`);
+    files.splice(config.maxFiles);
+  }
+
+  for (const file of files) {
+    if (file.content && file.content.length > config.maxFileChars) {
+      warnings.push(`File ${file.path || 'unknown'} was truncated to ${config.maxFileChars} characters. (maxFileChars=${config.maxFileChars})`);
+      file.content = file.content.slice(0, config.maxFileChars);
+    }
+  }
+
+  if (logs.length > config.maxLogChars) {
+    warnings.push(`Logs were truncated to ${config.maxLogChars} characters. (maxLogChars=${config.maxLogChars})`);
+    logs = logs.slice(0, config.maxLogChars);
+  }
+
+  // Helper: count all input characters
+  function countInputChars() {
+    let total = input.question.length;
+    if (context) total += context.length;
+    if (projectSummary) total += projectSummary.length;
+    if (taskSummary) total += taskSummary.length;
+    if (logs) total += logs.length;
+    for (const file of files) {
+      total += file.content ? file.content.length : 0;
+    }
+    return total;
+  }
+
+  // Step 2 — If still over global limit, trim droppable sections
+  let remaining = countInputChars();
+
+  if (remaining > config.maxInputChars && context) {
+    const allowed = Math.max(0, config.maxInputChars - remaining + context.length);
+    if (allowed < context.length) {
+      context = context.slice(0, allowed);
+      warnings.push(`Context was trimmed to ${allowed} characters. (budget exceeded)`);
+      remaining = countInputChars();
+    }
+  }
+
+  if (remaining > config.maxInputChars && projectSummary) {
+    const allowed = Math.max(0, config.maxInputChars - remaining + projectSummary.length);
+    if (allowed < projectSummary.length) {
+      projectSummary = projectSummary.slice(0, allowed);
+      warnings.push(`Project summary was trimmed to ${allowed} characters. (budget exceeded)`);
+      remaining = countInputChars();
+    }
+  }
+
+  if (remaining > config.maxInputChars && taskSummary) {
+    const allowed = Math.max(0, config.maxInputChars - remaining + taskSummary.length);
+    if (allowed < taskSummary.length) {
+      taskSummary = taskSummary.slice(0, allowed);
+      warnings.push(`Task summary was trimmed to ${allowed} characters. (budget exceeded)`);
+      remaining = countInputChars();
+    }
+  }
+
+  // Step 3 — Final check: if question alone or question + hard-limited files/logs exceeds limit, reject
+  remaining = countInputChars();
+
+  if (remaining > config.maxInputChars) {
+    return {
+      ok: false,
+      error:
+        'Input is too large for a focused review. Please retry with only the specific files, diff, or error section relevant to the question.',
+      warnings,
+      input: null,
+    };
+  }
+
+  // Build trimmed input object (only include non-empty optional fields)
+  const trimmedInput = { question: input.question };
+  if (context.length > 0) trimmedInput.context = context;
+  if (projectSummary.length > 0) trimmedInput.projectSummary = projectSummary;
+  if (taskSummary.length > 0) trimmedInput.taskSummary = taskSummary;
+  if (files.length > 0) trimmedInput.relevantFiles = files;
+  if (logs.length > 0) trimmedInput.logs = logs;
+
+  return { ok: true, input: trimmedInput, warnings };
+}