fix: support Magistral [THINK]...[/THINK] reasoning tags

src/api/providers/native-ollama.ts

@@ -6,6 +6,7 @@ import { BaseProvider } from "./base-provider"
 import type { ApiHandlerOptions } from "../../shared/api"
 import { getOllamaModels } from "./fetchers/ollama"
 import { XmlMatcher } from "../../utils/xml-matcher"
+import { SquareBracketMatcher } from "../../utils/square-bracket-matcher"
 import type { SingleCompletionHandler, ApiHandlerCreateMessageMetadata } from "../index"
 
 interface OllamaChatOptions {
@@ -173,20 +174,32 @@ export class NativeOllamaHandler extends BaseProvider implements SingleCompletio
 		const client = this.ensureClient()
 		const { id: modelId, info: modelInfo } = await this.fetchModel()
 		const useR1Format = modelId.toLowerCase().includes("deepseek-r1")
+		const useMagistralFormat = modelId.toLowerCase().includes("magistral")
 
 		const ollamaMessages: Message[] = [
 			{ role: "system", content: systemPrompt },
 			...convertToOllamaMessages(messages),
 		]
 
-		const matcher = new XmlMatcher(
-			"think",
-			(chunk) =>
-				({
-					type: chunk.matched ? "reasoning" : "text",
-					text: chunk.data,
-				}) as const,
-		)
+		// Magistral models use square bracket syntax [THINK]...[/THINK] for reasoning blocks
+		// instead of the XML-style <think>...</think> tags used by other models
+		const matcher = useMagistralFormat
+			? new SquareBracketMatcher(
+					"THINK",
+					(chunk) =>
+						({
+							type: chunk.matched ? "reasoning" : "text",
+							text: chunk.data,
+						}) as const,
+				)
+			: new XmlMatcher(
+					"think",
+					(chunk) =>
+						({
+							type: chunk.matched ? "reasoning" : "text",
+							text: chunk.data,
+						}) as const,
+				)
 
 		try {
 			// Build options object conditionally

src/utils/__tests__/square-bracket-matcher.spec.ts

@@ -0,0 +1,194 @@
+import { SquareBracketMatcher } from "../square-bracket-matcher"
+
+describe("SquareBracketMatcher", () => {
+	it("matches square bracket tags at position 0", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[THINK]data[/THINK]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "data",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles uppercase tag names", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[THINK]reasoning content[/THINK]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "reasoning content",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles lowercase tag names", () => {
+		const matcher = new SquareBracketMatcher("think")
+		const chunks = [...matcher.update("[think]reasoning content[/think]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "reasoning content",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles mixed content", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("Before [THINK]reasoning[/THINK] After"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "Before ",
+				matched: false,
+			},
+			{
+				data: "reasoning",
+				matched: true,
+			},
+			{
+				data: " After",
+				matched: false,
+			},
+		])
+	})
+
+	it("handles streaming push", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [
+			...matcher.update("["),
+			...matcher.update("THINK"),
+			...matcher.update("]"),
+			...matcher.update("reasoning"),
+			...matcher.update(" content"),
+			...matcher.update("[/"),
+			...matcher.update("THINK"),
+			...matcher.update("]"),
+			...matcher.final(),
+		]
+		expect(chunks).toEqual([
+			{
+				data: "reasoning content",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles nested tags", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[THINK]X[THINK]Y[/THINK]Z[/THINK]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "X[THINK]Y[/THINK]Z",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles invalid tag format", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[INVALID]data[/INVALID]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "[INVALID]data[/INVALID]",
+				matched: false,
+			},
+		])
+	})
+
+	it("handles unclosed tags", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[THINK]data"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "data",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles wrong matching position", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("prefix[THINK]data[/THINK]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "prefix",
+				matched: false,
+			},
+			{
+				data: "data",
+				matched: true,
+			},
+		])
+	})
+
+	it("handles multiple sequential tags", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const chunks = [...matcher.update("[THINK]first[/THINK] middle [THINK]second[/THINK]"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "first",
+				matched: true,
+			},
+			{
+				data: " middle ",
+				matched: false,
+			},
+			{
+				data: "second",
+				matched: true,
+			},
+		])
+	})
+
+	it("transforms output when transform function is provided", () => {
+		const matcher = new SquareBracketMatcher("THINK", (chunk) => ({
+			type: chunk.matched ? "reasoning" : "text",
+			text: chunk.data,
+		}))
+		const chunks = [...matcher.update("Before [THINK]reasoning[/THINK] After"), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				type: "text",
+				text: "Before ",
+			},
+			{
+				type: "reasoning",
+				text: "reasoning",
+			},
+			{
+				type: "text",
+				text: " After",
+			},
+		])
+	})
+
+	it("handles Magistral-style reasoning blocks", () => {
+		const matcher = new SquareBracketMatcher("THINK")
+		const input = `Let me analyze this problem.
+
+[THINK]
+I need to understand what the user is asking for.
+They want to fix an issue with Magistral model's reasoning tags.
+The tags use square brackets instead of angle brackets.
+[/THINK]
+
+Based on my analysis, here's the solution...`
+
+		const chunks = [...matcher.update(input), ...matcher.final()]
+		expect(chunks).toEqual([
+			{
+				data: "Let me analyze this problem.\n\n",
+				matched: false,
+			},
+			{
+				data: "\nI need to understand what the user is asking for.\nThey want to fix an issue with Magistral model's reasoning tags.\nThe tags use square brackets instead of angle brackets.\n",
+				matched: true,
+			},
+			{
+				data: "\n\nBased on my analysis, here's the solution...",
+				matched: false,
+			},
+		])
+	})
+})

src/utils/square-bracket-matcher.ts

@@ -0,0 +1,141 @@
+export interface SquareBracketMatcherResult {
+	matched: boolean
+	data: string
+}
+
+/**
+ * Matcher for square bracket tags like [THINK]...[/THINK]
+ * Used by models like Magistral that use square bracket syntax instead of angle brackets
+ */
+export class SquareBracketMatcher<Result = SquareBracketMatcherResult> {
+	private buffer = ""
+	private insideTag = false
+	private tagDepth = 0
+	private results: Result[] = []
+
+	constructor(
+		readonly tagName: string,
+		readonly transform?: (chunks: SquareBracketMatcherResult) => Result,
+		readonly position = 0,
+	) {}
+
+	private emit(matched: boolean, data: string) {
+		if (!data) return
+		const chunk: SquareBracketMatcherResult = { matched, data }
+		this.results.push(this.transform ? this.transform(chunk) : (chunk as Result))
+	}
+
+	private processComplete() {
+		const openTag = `[${this.tagName}]`
+		const closeTag = `[/${this.tagName}]`
+		let processed = false
+
+		while (true) {
+			if (!this.insideTag) {
+				// Look for opening tag
+				const openIndex = this.buffer.indexOf(openTag)
+				if (openIndex === -1) {
+					// No opening tag found
+					break
+				}
+
+				if (openIndex > 0) {
+					// Emit text before tag
+					this.emit(false, this.buffer.substring(0, openIndex))
+					this.buffer = this.buffer.substring(openIndex)
+					processed = true
+				}
+
+				// Now we have opening tag at start
+				this.buffer = this.buffer.substring(openTag.length)
+				this.insideTag = true
+				this.tagDepth = 1
+				processed = true
+			} else {
+				// Inside tag, look for closing tag
+				let pos = 0
+				let contentStart = 0
+
+				while (pos < this.buffer.length) {
+					const nextOpen = this.buffer.indexOf(openTag, pos)
+					const nextClose = this.buffer.indexOf(closeTag, pos)
+
+					if (nextClose === -1) {
+						// No closing tag found yet
+						break
+					}
+
+					if (nextOpen !== -1 && nextOpen < nextClose) {
+						// Found nested opening tag
+						this.tagDepth++
+						pos = nextOpen + openTag.length
+					} else {
+						// Found closing tag
+						this.tagDepth--
+						if (this.tagDepth === 0) {
+							// Complete match found
+							const content = this.buffer.substring(contentStart, nextClose)
+							this.emit(true, content)
+							this.buffer = this.buffer.substring(nextClose + closeTag.length)
+							this.insideTag = false
+							processed = true
+							break
+						} else {
+							// Still nested
+							pos = nextClose + closeTag.length
+						}
+					}
+				}
+
+				if (this.insideTag) {
+					// Still inside tag, no complete match yet
+					break
+				}
+			}
+		}
+
+		return processed
+	}
+
+	update(chunk: string): Result[] {
+		this.buffer += chunk
+		this.results = []
+
+		// Process any complete tag pairs
+		this.processComplete()
+
+		// For streaming, only emit unmatched text if we're sure it won't be part of a tag
+		if (!this.insideTag && this.buffer && !this.buffer.includes("[")) {
+			// No potential tags, emit as text
+			this.emit(false, this.buffer)
+			this.buffer = ""
+		}
+
+		const results = this.results
+		this.results = []
+		return results
+	}
+
+	final(chunk?: string): Result[] {
+		if (chunk) {
+			this.buffer += chunk
+		}
+
+		this.results = []
+
+		// Process any remaining complete pairs
+		this.processComplete()
+
+		// Emit any remaining buffer
+		if (this.buffer) {
+			this.emit(this.insideTag, this.buffer)
+			this.buffer = ""
+		}
+
+		const results = this.results
+		this.results = []
+		this.insideTag = false
+		this.tagDepth = 0
+		return results
+	}
+}