feat: add tags workflow

README.md

@@ -14,7 +14,8 @@ cloud, no server: git-friendly, editable in any editor.
 - **Dashboard** — task list + description (filters, scope, sort, group)
 - **Kanban** — status columns, drag-and-drop, create-in-column
 - **Commands** — create / open / change status / delete
-- **In-editor** — frontmatter lint + status/priority Quick Pick (decorations)
+- **In-editor** — frontmatter lint + status/priority/tags/assignee actions
+- **Project tags** — catalog in task folder `config.yml`
 - **Two stores** — project folder (workspace) and global folder (shared on the
   machine)
 
@@ -119,6 +120,26 @@ Task description in markdown…
 One file per task (`*.xflow.md`). File name is derived from the title (slug).
 `title` max length: 80 characters.
 
+### Project config (`config.yml` in the task folder)
+
+Default layout:
+
+```text
+.xflow/
+  config.yml          # project tags catalog
+  fix-login.xflow.md
+```
+
+```yaml
+# .xflow/config.yml
+tags:
+  - bug
+  - frontend
+```
+
+If `config.yml` exists, tags on a task that are **not** in the catalog show as
+warnings. Hover `tags` → **Edit tags…** / **Add tag to project**.
+
 ## Dashboard
 
 - Search title/body; status/priority chips; group none/status/priority

README_ru.md

@@ -15,7 +15,8 @@ extension.
 - **Dashboard** — список + описание задачи (фильтры, scope, sort, group)
 - **Kanban** — колонки по статусу, drag-and-drop, create в колонке
 - **Команды** — create / open / change status / delete
-- **In-editor** — lint frontmatter + Quick Pick status/priority (decorations)
+- **In-editor** — lint frontmatter + status/priority/tags/assignee
+- **Теги проекта** — каталог в `config.yml` папки задач
 - **Два хранилища** — проектное (в workspace) и глобальное (общая папка на
   машине)
 
@@ -119,6 +120,26 @@ updated: 2026-07-12T10:00:00.000Z
 Один файл — одна задача (`*.xflow.md`). Имя файла строится из title (slug).
 Макс. длина `title`: 80 символов.
 
+### Конфиг проекта (`config.yml` в папке задач)
+
+По умолчанию:
+
+```text
+.xflow/
+  config.yml
+  fix-login.xflow.md
+```
+
+```yaml
+# .xflow/config.yml
+tags:
+  - bug
+  - frontend
+```
+
+Если `config.yml` есть, теги задачи вне каталога — warning. Hover на `tags` →
+**Edit tags…** / **Add tag to project**.
+
 ## Dashboard
 
 - Поиск по title/body, chips status/priority, group none/status/priority

package.json

@@ -77,6 +77,14 @@
 				"command": "xboctukFlow.setAssigneeMe",
 				"title": "XBOCTuK Flow: Set Assignee to Me"
 			},
+			{
+				"command": "xboctukFlow.editTaskTags",
+				"title": "XBOCTuK Flow: Edit Tags (in file)"
+			},
+			{
+				"command": "xboctukFlow.addTagToProject",
+				"title": "XBOCTuK Flow: Add Tag to Project"
+			},
 			{
 				"command": "xboctukFlow.openDashboard",
 				"title": "XBOCTuK Flow: Open Dashboard",

src/commands/addProjectTag.test.ts

@@ -0,0 +1,75 @@
+import { beforeEach, describe, expect, it } from "vitest";
+import { AppErrorVariant } from "@/error";
+import { getProjectConfigPath } from "@/model/projectConfig";
+import { InMemoryFileSystem } from "../../tests/helpers/InMemoryFileSystem";
+import { addProjectTag } from "./addProjectTag";
+import { loadProjectConfig } from "./loadProjectConfig";
+
+describe("addProjectTag", () => {
+	const folder = "/ws/.xflow";
+	let fs: InMemoryFileSystem;
+
+	beforeEach(() => {
+		fs = new InMemoryFileSystem();
+	});
+
+	it("creates config.yml and adds the tag", async () => {
+		const result = await addProjectTag(fs, {
+			folderPath: folder,
+			tag: "bug",
+		});
+		expect(result.isOk()).toBe(true);
+		if (result.isErr()) return;
+		expect(result.value.added).toBe(true);
+		expect(result.value.config.tags).toEqual(["bug"]);
+
+		const loaded = await loadProjectConfig(fs, folder);
+		expect(loaded._unsafeUnwrap().exists).toBe(true);
+		expect(loaded._unsafeUnwrap().config.tags).toEqual(["bug"]);
+		expect(await fs.readFile(getProjectConfigPath(folder))).toContain("bug");
+	});
+
+	it("is idempotent for an existing tag", async () => {
+		await addProjectTag(fs, { folderPath: folder, tag: "bug" });
+		const result = await addProjectTag(fs, {
+			folderPath: folder,
+			tag: "bug",
+		});
+		expect(result.isOk()).toBe(true);
+		if (result.isErr()) return;
+		expect(result.value.added).toBe(false);
+		expect(result.value.config.tags).toEqual(["bug"]);
+	});
+
+	it("appends a new tag", async () => {
+		await addProjectTag(fs, { folderPath: folder, tag: "bug" });
+		const result = await addProjectTag(fs, {
+			folderPath: folder,
+			tag: "frontend",
+		});
+		expect(result._unsafeUnwrap().config.tags).toEqual(["bug", "frontend"]);
+	});
+
+	it("trims tag and rejects empty", async () => {
+		const empty = await addProjectTag(fs, {
+			folderPath: folder,
+			tag: "   ",
+		});
+		expect(empty.isErr()).toBe(true);
+		if (empty.isOk()) return;
+		expect(empty.error.variant).toBe(AppErrorVariant.EMPTY_TAG);
+
+		const trimmed = await addProjectTag(fs, {
+			folderPath: folder,
+			tag: "  docs  ",
+		});
+		expect(trimmed._unsafeUnwrap().config.tags).toEqual(["docs"]);
+	});
+
+	it("rejects missing folder", async () => {
+		const result = await addProjectTag(fs, { tag: "bug" });
+		expect(result.isErr()).toBe(true);
+		if (result.isOk()) return;
+		expect(result.error.variant).toBe(AppErrorVariant.NO_FOLDER);
+	});
+});

src/commands/addProjectTag.ts

@@ -0,0 +1,69 @@
+import { errAsync, okAsync, ResultAsync } from "neverthrow";
+import { appError, AppError, AppErrorVariant } from "@/error";
+import {
+	getProjectConfigPath,
+	normalizeTag,
+	type ProjectConfig,
+} from "@/model/projectConfig";
+import { IFileSystem } from "@/ports";
+import { serializeProjectConfig } from "@/projectConfig/serializeProjectConfig";
+import { loadProjectConfig } from "./loadProjectConfig";
+
+export type AddProjectTagInput = {
+	folderPath?: string;
+	tag?: string;
+};
+
+export type AddProjectTagValue = {
+	config: ProjectConfig;
+	/** True if the tag was newly added. */
+	added: boolean;
+	path: string;
+};
+
+export function addProjectTag(
+	fs: IFileSystem,
+	input: AddProjectTagInput,
+): ResultAsync<AddProjectTagValue, AppError> {
+	if (input.folderPath === undefined || input.folderPath === "") {
+		return errAsync(appError(AppErrorVariant.NO_FOLDER));
+	}
+	if (input.tag === undefined) {
+		return errAsync(appError(AppErrorVariant.EMPTY_TAG));
+	}
+
+	const tag = normalizeTag(input.tag);
+	if (!tag) {
+		return errAsync(appError(AppErrorVariant.EMPTY_TAG));
+	}
+
+	const folderPath = input.folderPath;
+	const path = getProjectConfigPath(folderPath);
+
+	return loadProjectConfig(fs, folderPath).andThen((loaded) => {
+		if (loaded.config.tags.includes(tag)) {
+			return okAsync({
+				config: loaded.config,
+				added: false,
+				path,
+			});
+		}
+
+		const config: ProjectConfig = {
+			tags: [...loaded.config.tags, tag],
+		};
+		const content = serializeProjectConfig(config);
+
+		return ResultAsync.fromPromise(
+			fs.mkdir(folderPath).then(() => fs.writeFile(path, content)),
+			(error) =>
+				appError(AppErrorVariant.INVALID_PROJECT_CONFIG, {
+					detail: error instanceof Error ? error.message : "write failed",
+				}),
+		).map(() => ({
+			config,
+			added: true,
+			path,
+		}));
+	});
+}

src/commands/loadProjectConfig.test.ts

@@ -0,0 +1,54 @@
+import { beforeEach, describe, expect, it } from "vitest";
+import { AppErrorVariant } from "@/error";
+import { getProjectConfigPath } from "@/model/projectConfig";
+import { InMemoryFileSystem } from "../../tests/helpers/InMemoryFileSystem";
+import { loadProjectConfig } from "./loadProjectConfig";
+
+describe("loadProjectConfig", () => {
+	const folder = "/ws/.xflow";
+	let fs: InMemoryFileSystem;
+
+	beforeEach(() => {
+		fs = new InMemoryFileSystem();
+	});
+
+	it("returns exists:false and empty tags when config.yml is missing", async () => {
+		const result = await loadProjectConfig(fs, folder);
+		expect(result.isOk()).toBe(true);
+		if (result.isErr()) return;
+		expect(result.value.exists).toBe(false);
+		expect(result.value.config.tags).toEqual([]);
+		expect(result.value.path).toBe(getProjectConfigPath(folder));
+	});
+
+	it("loads tags when config.yml exists", async () => {
+		await fs.mkdir(folder);
+		await fs.writeFile(
+			getProjectConfigPath(folder),
+			"tags:\n  - bug\n  - frontend\n",
+		);
+
+		const result = await loadProjectConfig(fs, folder);
+		expect(result.isOk()).toBe(true);
+		if (result.isErr()) return;
+		expect(result.value.exists).toBe(true);
+		expect(result.value.config.tags).toEqual(["bug", "frontend"]);
+	});
+
+	it("rejects missing folder path", async () => {
+		const result = await loadProjectConfig(fs, undefined);
+		expect(result.isErr()).toBe(true);
+		if (result.isOk()) return;
+		expect(result.error.variant).toBe(AppErrorVariant.NO_FOLDER);
+	});
+
+	it("rejects invalid config content", async () => {
+		await fs.mkdir(folder);
+		await fs.writeFile(getProjectConfigPath(folder), "tags: [\n");
+
+		const result = await loadProjectConfig(fs, folder);
+		expect(result.isErr()).toBe(true);
+		if (result.isOk()) return;
+		expect(result.error.variant).toBe(AppErrorVariant.INVALID_PROJECT_CONFIG);
+	});
+});

src/commands/loadProjectConfig.ts

@@ -0,0 +1,53 @@
+import { errAsync, okAsync, ResultAsync } from "neverthrow";
+import { appError, AppError, AppErrorVariant } from "@/error";
+import {
+	EMPTY_PROJECT_CONFIG,
+	getProjectConfigPath,
+	type ProjectConfig,
+} from "@/model/projectConfig";
+import { IFileSystem } from "@/ports";
+import { parseProjectConfig } from "@/projectConfig/parseProjectConfig";
+
+export type LoadProjectConfigValue = {
+	config: ProjectConfig;
+	/** False when config.yml is missing (catalog checks should be skipped). */
+	exists: boolean;
+	path: string;
+};
+
+export function loadProjectConfig(
+	fs: IFileSystem,
+	folderPath: string | undefined,
+): ResultAsync<LoadProjectConfigValue, AppError> {
+	if (folderPath === undefined || folderPath === "") {
+		return errAsync(appError(AppErrorVariant.NO_FOLDER));
+	}
+
+	const path = getProjectConfigPath(folderPath);
+
+	return ResultAsync.fromSafePromise(
+		fs.readFile(path).then(
+			(content) => ({ found: true as const, content }),
+			() => ({ found: false as const }),
+		),
+	).andThen((read) => {
+		if (!read.found) {
+			return okAsync({
+				config: { ...EMPTY_PROJECT_CONFIG },
+				exists: false,
+				path,
+			});
+		}
+
+		const parsed = parseProjectConfig(read.content);
+		if (parsed.isErr()) {
+			return errAsync(parsed.error);
+		}
+
+		return okAsync({
+			config: parsed.value,
+			exists: true,
+			path,
+		});
+	});
+}

src/error.ts

@@ -8,6 +8,8 @@ export const AppErrorVariant = {
 	NOT_FOUND: "not-found",
 	INVALID_MESSAGE: "invalid-message",
 	INVALID_TASK_FILE: "invalid-task-file",
+	INVALID_PROJECT_CONFIG: "invalid-project-config",
+	EMPTY_TAG: "empty-tag",
 } as const;
 
 export type AppErrorVariant =
@@ -31,6 +33,8 @@ const APP_ERROR_MESSAGES: Record<AppErrorVariant, string> = {
 	[AppErrorVariant.NOT_FOUND]: "Task not found: {id}",
 	[AppErrorVariant.INVALID_MESSAGE]: "Invalid message: {detail}",
 	[AppErrorVariant.INVALID_TASK_FILE]: "Invalid task file: {detail}",
+	[AppErrorVariant.INVALID_PROJECT_CONFIG]: "Invalid project config: {detail}",
+	[AppErrorVariant.EMPTY_TAG]: "Tag is empty",
 };
 
 export function formatMessage(

src/extension.ts

@@ -48,13 +48,14 @@ export function activate(context: vscode.ExtensionContext) {
 	statusBarItem.show();
 	context.subscriptions.push(statusBarItem);
 
-	registerTaskDiagnostics(context);
+	registerTaskDiagnostics(context, { fs: fileSystem, config });
 	registerTaskDecorations(context);
 
 	registerTaskCommands(context, {
 		repo,
 		config,
 		tree,
+		fs: fileSystem,
 		onTasksMutated: () => {
 			TaskDashboardPanel.refreshIfOpen();
 			TaskKanbanPanel.refreshIfOpen();

src/frontmatter/frontmatterFields.test.ts

@@ -1,11 +1,17 @@
 import { describe, expect, it } from "vitest";
-import { findFieldRange, replaceFrontmatterField } from "./frontmatterFields";
+import {
+	findFieldRange,
+	formatTagsYamlValue,
+	replaceFrontmatterField,
+	setFrontmatterTags,
+} from "./frontmatterFields";
 
 const sample = `---
 id: abc
 title: Hello
 status: todo
 priority: medium
+tags: [old]
 ---
 
 Body
@@ -47,3 +53,26 @@ describe("findFieldRange", () => {
 		expect(line.slice(range!.startCol, range!.endCol)).toBe("todo");
 	});
 });
+
+describe("formatTagsYamlValue", () => {
+	it("formats empty and simple lists", () => {
+		expect(formatTagsYamlValue([])).toBe("[]");
+		expect(formatTagsYamlValue(["bug", "frontend"])).toBe(
+			"[bug, frontend]",
+		);
+	});
+
+	it("quotes tags with spaces", () => {
+		expect(formatTagsYamlValue(["my tag"])).toBe('["my tag"]');
+	});
+});
+
+describe("setFrontmatterTags", () => {
+	it("replaces the tags line", () => {
+		const result = setFrontmatterTags(sample, ["bug", "docs"]);
+		expect(result.ok).toBe(true);
+		if (!result.ok) return;
+		expect(result.content).toContain("tags: [bug, docs]");
+		expect(result.content).not.toContain("tags: [old]");
+	});
+});

src/frontmatter/frontmatterFields.ts

@@ -1,3 +1,4 @@
+import { yamlInlineScalar } from "@/utils/yamlScalar";
 import {
 	extractFrontmatterBlock,
 	findFieldLineRange,
@@ -12,6 +13,21 @@ export type ReplaceFrontmatterFieldResult =
 	| { ok: true; content: string; range: TextRange }
 	| { ok: false; reason: "no-frontmatter" | "no-field" };
 
+/** Inline YAML list for frontmatter `tags: […]`. */
+export function formatTagsYamlValue(tags: string[]): string {
+	if (tags.length === 0) {
+		return "[]";
+	}
+	return `[${tags.map((t) => yamlInlineScalar(t)).join(", ")}]`;
+}
+
+export function setFrontmatterTags(
+	content: string,
+	tags: string[],
+): ReplaceFrontmatterFieldResult {
+	return replaceFrontmatterField(content, "tags", formatTagsYamlValue(tags));
+}
+
 /**
  * Replace a scalar frontmatter field value on its line.
  * Does not re-serialize YAML; only rewrites the value after `:`.

src/frontmatter/parseTaskTags.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { parseTaskTags } from "./parseTaskTags";
+
+const sample = `---
+id: "a"
+title: T
+status: todo
+priority: medium
+tags: [bug, frontend]
+assignee: ""
+created: 2026-01-01T00:00:00.000Z
+updated: 2026-01-01T00:00:00.000Z
+---
+
+body
+`;
+
+describe("parseTaskTags", () => {
+	it("reads tags from frontmatter", () => {
+		expect(parseTaskTags(sample)).toEqual(["bug", "frontend"]);
+	});
+
+	it("returns empty when tags missing", () => {
+		const content = sample.replace("tags: [bug, frontend]\n", "");
+		expect(parseTaskTags(content)).toEqual([]);
+	});
+
+	it("returns empty for invalid content", () => {
+		expect(parseTaskTags("not a task")).toEqual([]);
+	});
+});

src/frontmatter/parseTaskTags.ts

@@ -0,0 +1,23 @@
+import * as yaml from "js-yaml";
+import { extractFrontmatterBlock } from "./frontmatterBlock";
+
+/** Read current tags array from task file content (empty if missing/invalid). */
+export function parseTaskTags(content: string): string[] {
+	const block = extractFrontmatterBlock(content);
+	if (!block || block.closeLine < 0) {
+		return [];
+	}
+	try {
+		const data = yaml.load(block.yaml);
+		if (!data || typeof data !== "object" || Array.isArray(data)) {
+			return [];
+		}
+		const tags = (data as Record<string, unknown>).tags;
+		if (!Array.isArray(tags)) {
+			return [];
+		}
+		return tags.filter((t): t is string => typeof t === "string");
+	} catch {
+		return [];
+	}
+}

src/frontmatter/validateFrontmatter.test.ts

@@ -93,4 +93,38 @@ title: [unterminated
 		const issues = validateFrontmatter(content);
 		expect(issues.some((i) => /yaml/i.test(i.message))).toBe(true);
 	});
+
+	it("does not warn about unknown tags when knownTags is omitted", () => {
+		const issues = validateFrontmatter(valid);
+		expect(issues.filter((i) => i.field === "tags")).toEqual([]);
+	});
+
+	it("warns when a tag is not in knownTags", () => {
+		const content = valid.replace("tags: [bug]", "tags: [bug, nope]");
+		const issues = validateFrontmatter(content, { knownTags: ["bug"] });
+		const unknown = issues.filter(
+			(i) => i.field === "tags" && i.severity === "warning",
+		);
+		expect(unknown).toHaveLength(1);
+		expect(unknown[0].message).toMatch(/nope/i);
+	});
+
+	it("does not warn when all tags are known", () => {
+		const issues = validateFrontmatter(valid, {
+			knownTags: ["bug", "frontend"],
+		});
+		expect(issues.filter((i) => i.severity === "warning")).toEqual([]);
+	});
+
+	it("warns for every tag when knownTags is empty array (config exists)", () => {
+		const issues = validateFrontmatter(valid, { knownTags: [] });
+		expect(
+			issues.some(
+				(i) =>
+					i.field === "tags" &&
+					i.severity === "warning" &&
+					/bug/i.test(i.message),
+			),
+		).toBe(true);
+	});
 });

src/frontmatter/validateFrontmatter.ts

@@ -47,11 +47,50 @@ function fieldRangeOrBlock(
 	return findFieldRange(content, key) ?? blockRange;
 }
 
+/** Best-effort range of a tag token inside the tags field value. */
+export function findTagTokenRange(
+	content: string,
+	tag: string,
+): TextRange | undefined {
+	const fieldRange = findFieldRange(content, "tags");
+	if (!fieldRange) return undefined;
+
+	const lines = content.split(/\r?\n/);
+	const line = lines[fieldRange.startLine] ?? "";
+	const value = line.slice(fieldRange.startCol);
+	const escaped = tag.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+	const re = new RegExp(
+		`(?<![\\w-])(?:"${escaped}"|'${escaped}'|${escaped})(?![\\w-])`,
+	);
+	const match = re.exec(value);
+	if (!match || match.index === undefined) {
+		return fieldRange;
+	}
+	const startCol = fieldRange.startCol + match.index;
+	return {
+		startLine: fieldRange.startLine,
+		startCol,
+		endLine: fieldRange.startLine,
+		endCol: startCol + match[0].length,
+	};
+}
+
+export type ValidateFrontmatterOptions = {
+	/**
+	 * When set (including empty array), tags not in this list produce warnings.
+	 * When undefined, catalog checks are skipped (no project config file).
+	 */
+	knownTags?: string[];
+};
+
 /**
  * Validate task file frontmatter. Pure — no vscode.
  * Ranges are 0-based line/column.
  */
-export function validateFrontmatter(content: string): FrontmatterIssue[] {
+export function validateFrontmatter(
+	content: string,
+	options: ValidateFrontmatterOptions = {},
+): FrontmatterIssue[] {
 	const issues: FrontmatterIssue[] = [];
 	const block = extractFrontmatterBlock(content);
 
@@ -209,6 +248,20 @@ export function validateFrontmatter(content: string): FrontmatterIssue[] {
 				severity: "error",
 				range: fieldRangeOrBlock(content, "tags", blockRange),
 			});
+		} else if (options.knownTags !== undefined) {
+			const known = new Set(options.knownTags);
+			for (const tag of record.tags as string[]) {
+				if (!known.has(tag)) {
+					issues.push({
+						field: "tags",
+						message: `Unknown tag "${tag}"; add it to project config or pick from catalog`,
+						severity: "warning",
+						range:
+							findTagTokenRange(content, tag) ??
+							fieldRangeOrBlock(content, "tags", blockRange),
+					});
+				}
+			}
 		}
 	}
 

src/model/projectConfig.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from "vitest";
+import {
+	EMPTY_PROJECT_CONFIG,
+	getProjectConfigPath,
+	normalizeTag,
+	TASK_FOLDER_CONFIG_FILENAME,
+} from "./projectConfig";
+
+describe("projectConfig model", () => {
+	it("uses config.yml as the filename inside the task folder", () => {
+		expect(TASK_FOLDER_CONFIG_FILENAME).toBe("config.yml");
+	});
+
+	it("joins folder path with config.yml", () => {
+		expect(getProjectConfigPath("/ws/.xflow")).toBe("/ws/.xflow/config.yml");
+		expect(getProjectConfigPath("C:\\proj\\.xflow")).toMatch(
+			/config\.yml$/,
+		);
+	});
+
+	it("empty config has no tags", () => {
+		expect(EMPTY_PROJECT_CONFIG).toEqual({ tags: [] });
+	});
+
+	it("normalizeTag trims and rejects empty", () => {
+		expect(normalizeTag("  bug  ")).toBe("bug");
+		expect(normalizeTag("   ")).toBeUndefined();
+		expect(normalizeTag("")).toBeUndefined();
+	});
+});

src/model/projectConfig.ts

@@ -0,0 +1,22 @@
+/** Config file name inside a task folder (project or global). */
+export const TASK_FOLDER_CONFIG_FILENAME = "config.yml";
+
+export type ProjectConfig = {
+	tags: string[];
+};
+
+export const EMPTY_PROJECT_CONFIG: ProjectConfig = {
+	tags: [],
+};
+
+/** Absolute/joined path to config.yml in a task folder. */
+export function getProjectConfigPath(folderPath: string): string {
+	const base = folderPath.replace(/\\/g, "/").replace(/\/$/, "");
+	return `${base}/${TASK_FOLDER_CONFIG_FILENAME}`;
+}
+
+/** Normalize a tag: trim. Empty after trim → undefined. */
+export function normalizeTag(value: string): string | undefined {
+	const tag = value.trim();
+	return tag.length > 0 ? tag : undefined;
+}

src/projectConfig/parseProjectConfig.test.ts

@@ -0,0 +1,40 @@
+import { describe, expect, it } from "vitest";
+import { AppErrorVariant } from "@/error";
+import { parseProjectConfig } from "./parseProjectConfig";
+
+describe("parseProjectConfig", () => {
+	it("parses tags list", () => {
+		const result = parseProjectConfig("tags:\n  - bug\n  - frontend\n");
+		expect(result.isOk()).toBe(true);
+		if (result.isErr()) return;
+		expect(result.value.tags).toEqual(["bug", "frontend"]);
+	});
+
+	it("accepts empty / missing tags", () => {
+		expect(parseProjectConfig("")._unsafeUnwrap().tags).toEqual([]);
+		expect(parseProjectConfig("tags: []\n")._unsafeUnwrap().tags).toEqual(
+			[],
+		);
+	});
+
+	it("dedupes and trims tags", () => {
+		const result = parseProjectConfig(
+			"tags:\n  - bug\n  -  bug  \n  - frontend\n",
+		);
+		expect(result._unsafeUnwrap().tags).toEqual(["bug", "frontend"]);
+	});
+
+	it("rejects invalid YAML", () => {
+		const result = parseProjectConfig("tags: [\n");
+		expect(result.isErr()).toBe(true);
+		if (result.isOk()) return;
+		expect(result.error.variant).toBe(AppErrorVariant.INVALID_PROJECT_CONFIG);
+	});
+
+	it("rejects non-string tags", () => {
+		const result = parseProjectConfig("tags:\n  - 1\n");
+		expect(result.isErr()).toBe(true);
+		if (result.isOk()) return;
+		expect(result.error.variant).toBe(AppErrorVariant.INVALID_PROJECT_CONFIG);
+	});
+});

src/projectConfig/parseProjectConfig.ts

@@ -0,0 +1,73 @@
+import * as yaml from "js-yaml";
+import { err, ok, Result } from "neverthrow";
+import { appError, AppError, AppErrorVariant } from "@/error";
+import {
+	EMPTY_PROJECT_CONFIG,
+	normalizeTag,
+	type ProjectConfig,
+} from "@/model/projectConfig";
+
+/**
+ * Parse task-folder config.yml content.
+ * Accepts missing/empty tags → [].
+ */
+export function parseProjectConfig(
+	content: string,
+): Result<ProjectConfig, AppError> {
+	if (content.trim() === "") {
+		return ok({ ...EMPTY_PROJECT_CONFIG });
+	}
+
+	let data: unknown;
+	try {
+		data = yaml.load(content);
+	} catch (error) {
+		const detail = error instanceof Error ? error.message : "invalid YAML";
+		return err(
+			appError(AppErrorVariant.INVALID_PROJECT_CONFIG, { detail }),
+		);
+	}
+
+	if (data === null || data === undefined) {
+		return ok({ ...EMPTY_PROJECT_CONFIG });
+	}
+
+	if (typeof data !== "object" || Array.isArray(data)) {
+		return err(
+			appError(AppErrorVariant.INVALID_PROJECT_CONFIG, {
+				detail: "root must be a mapping",
+			}),
+		);
+	}
+
+	const record = data as Record<string, unknown>;
+	if (record.tags === undefined) {
+		return ok({ tags: [] });
+	}
+
+	if (!Array.isArray(record.tags)) {
+		return err(
+			appError(AppErrorVariant.INVALID_PROJECT_CONFIG, {
+				detail: "tags must be an array of strings",
+			}),
+		);
+	}
+
+	const tags: string[] = [];
+	const seen = new Set<string>();
+	for (const item of record.tags) {
+		if (typeof item !== "string") {
+			return err(
+				appError(AppErrorVariant.INVALID_PROJECT_CONFIG, {
+					detail: "tags must be an array of strings",
+				}),
+			);
+		}
+		const tag = normalizeTag(item);
+		if (!tag || seen.has(tag)) continue;
+		seen.add(tag);
+		tags.push(tag);
+	}
+
+	return ok({ tags });
+}

src/projectConfig/serializeProjectConfig.test.ts

@@ -0,0 +1,19 @@
+import { describe, expect, it } from "vitest";
+import { parseProjectConfig } from "./parseProjectConfig";
+import { serializeProjectConfig } from "./serializeProjectConfig";
+
+describe("serializeProjectConfig", () => {
+	it("round-trips tags", () => {
+		const yaml = serializeProjectConfig({ tags: ["bug", "docs"] });
+		expect(yaml).toContain("bug");
+		expect(yaml).toContain("docs");
+		const parsed = parseProjectConfig(yaml);
+		expect(parsed._unsafeUnwrap().tags).toEqual(["bug", "docs"]);
+	});
+
+	it("serializes empty tags", () => {
+		const yaml = serializeProjectConfig({ tags: [] });
+		const parsed = parseProjectConfig(yaml);
+		expect(parsed._unsafeUnwrap().tags).toEqual([]);
+	});
+});

src/projectConfig/serializeProjectConfig.ts

@@ -0,0 +1,15 @@
+import * as yaml from "js-yaml";
+import type { ProjectConfig } from "@/model/projectConfig";
+
+export function serializeProjectConfig(config: ProjectConfig): string {
+	return yaml
+		.dump(
+			{ tags: config.tags },
+			{
+				lineWidth: -1,
+				forceQuotes: false,
+			},
+		)
+		.trimEnd()
+		.concat("\n");
+}

src/ui/editFrontmatterField.ts

@@ -1,14 +1,24 @@
 import * as vscode from "vscode";
+import { addProjectTag } from "@/commands/addProjectTag";
+import { loadProjectConfig } from "@/commands/loadProjectConfig";
+import { resolveTaskLocations } from "@/commands/resolveTaskLocations";
 import {
 	findFieldRange,
+	formatTagsYamlValue,
 	replaceFrontmatterField,
+	setFrontmatterTags,
 } from "@/frontmatter/frontmatterFields";
+import { parseTaskTags } from "@/frontmatter/parseTaskTags";
+import { normalizeTag } from "@/model/projectConfig";
 import {
 	isTaskFileName,
 	TASK_FILE_EXTENSION,
 	TASK_LANGUAGE_ID,
 } from "@/model/taskFile";
+import { IConfigProvider, IFileSystem } from "@/ports";
 import { getGitUserName, yamlInlineScalar } from "./getGitUserName";
+import { presentError } from "./presentError";
+import { resolveTaskFolderForPath } from "./resolveTaskFolder";
 import {
 	TASK_PRIORITY_LABELS,
 	TASK_PRIORITY_ORDER,
@@ -16,10 +26,16 @@ import {
 	TASK_STATUS_ORDER,
 } from "./taskLabels";
 
+export type FrontmatterEditDeps = {
+	fs: IFileSystem;
+	config: IConfigProvider;
+};
+
 export const EditableField = {
 	STATUS: "status",
 	PRIORITY: "priority",
 	ASSIGNEE: "assignee",
+	TAGS: "tags",
 } as const;
 
 export type EditableField = (typeof EditableField)[keyof typeof EditableField];
@@ -151,5 +167,253 @@ export async function runSetAssigneeMe(uriArg?: string): Promise<void> {
 		return;
 	}
 
-	await applyFieldValue(document, EditableField.ASSIGNEE, yamlInlineScalar(name));
+	await applyFieldValue(
+		document,
+		EditableField.ASSIGNEE,
+		yamlInlineScalar(name),
+	);
+}
+
+async function resolveTaskFolder(
+	document: vscode.TextDocument,
+	config: IConfigProvider,
+): Promise<string | undefined> {
+	const locations = resolveTaskLocations(config);
+	return resolveTaskFolderForPath(document.fileName, locations);
+}
+
+async function applyTags(
+	document: vscode.TextDocument,
+	tags: string[],
+): Promise<boolean> {
+	const text = document.getText();
+	const result = setFrontmatterTags(text, tags);
+	if (!result.ok) {
+		void vscode.window.showErrorMessage(
+			result.reason === "no-field"
+				? 'Field "tags" not found in frontmatter'
+				: "No YAML frontmatter in this file",
+		);
+		return false;
+	}
+
+	const valueRange = findFieldRange(text, EditableField.TAGS);
+	const value = formatTagsYamlValue(tags);
+	if (!valueRange) {
+		const full = new vscode.Range(
+			document.positionAt(0),
+			document.positionAt(text.length),
+		);
+		const edit = new vscode.WorkspaceEdit();
+		edit.replace(document.uri, full, result.content);
+		return vscode.workspace.applyEdit(edit);
+	}
+
+	const range = new vscode.Range(
+		valueRange.startLine,
+		valueRange.startCol,
+		valueRange.endLine,
+		valueRange.endCol,
+	);
+	const edit = new vscode.WorkspaceEdit();
+	edit.replace(document.uri, range, value);
+	return vscode.workspace.applyEdit(edit);
+}
+
+/**
+ * Multi-select tags from project config.
+ *
+ * - Type a name + Enter → add tag (selected), stay on Quick Pick
+ * - Enter on empty field → apply selection to task + config
+ * - Escape → cancel
+ */
+export async function runEditTaskTags(
+	deps: FrontmatterEditDeps,
+	uriArg?: string,
+): Promise<void> {
+	const document = await resolveDocument(uriArg);
+	if (!document) {
+		void vscode.window.showErrorMessage(
+			`Open a ${TASK_FILE_EXTENSION} task file first`,
+		);
+		return;
+	}
+
+	const folder = await resolveTaskFolder(document, deps.config);
+	if (!folder) {
+		void vscode.window.showErrorMessage(
+			"Task file is outside a configured task folder",
+		);
+		return;
+	}
+
+	const loaded = await loadProjectConfig(deps.fs, folder);
+	if (loaded.isErr()) {
+		presentError(loaded.error);
+		return;
+	}
+
+	const catalog = [...loaded.value.config.tags];
+	const current = parseTaskTags(document.getText());
+
+	type TagItem = vscode.QuickPickItem & { tag: string };
+
+	const selected = await new Promise<string[] | undefined>((resolve) => {
+		const qp = vscode.window.createQuickPick<TagItem>();
+		qp.canSelectMany = true;
+		qp.ignoreFocusOut = true;
+		qp.placeholder =
+			"Select tags · type name + Enter to add · empty Enter to apply · Esc to cancel";
+		qp.matchOnDescription = true;
+
+		const extraTags: string[] = [];
+		let selectedTags = new Set(current);
+		let accepted = false;
+		let syncingSelection = false;
+
+		const rebuild = (): void => {
+			const items: TagItem[] = [];
+			const seen = new Set<string>();
+			for (const tag of [...catalog, ...current, ...extraTags]) {
+				if (seen.has(tag)) continue;
+				seen.add(tag);
+				items.push({
+					label: tag,
+					description: catalog.includes(tag)
+						? undefined
+						: "will add to config",
+					tag,
+				});
+			}
+			syncingSelection = true;
+			qp.items = items;
+			qp.selectedItems = items.filter((item) => selectedTags.has(item.tag));
+			syncingSelection = false;
+		};
+
+		rebuild();
+
+		qp.onDidChangeSelection((items) => {
+			if (syncingSelection) return;
+			selectedTags = new Set(items.map((item) => item.tag));
+		});
+
+		qp.onDidAccept(() => {
+			const typed = normalizeTag(qp.value);
+			if (typed) {
+				if (!extraTags.includes(typed) && !catalog.includes(typed)) {
+					extraTags.push(typed);
+				}
+				selectedTags.add(typed);
+				qp.value = "";
+				rebuild();
+				return;
+			}
+
+			accepted = true;
+			const tags = [...selectedTags];
+			qp.hide();
+			qp.dispose();
+			resolve(tags);
+		});
+
+		qp.onDidHide(() => {
+			if (!accepted) {
+				qp.dispose();
+				resolve(undefined);
+			}
+		});
+
+		qp.show();
+	});
+
+	if (selected === undefined) return;
+
+	const catalogSet = new Set(catalog);
+	for (const tag of selected) {
+		if (catalogSet.has(tag)) continue;
+		const added = await addProjectTag(deps.fs, {
+			folderPath: folder,
+			tag,
+		});
+		if (added.isErr()) {
+			presentError(added.error);
+			return;
+		}
+		catalogSet.add(tag);
+	}
+
+	const ok = await applyTags(document, selected);
+	if (ok) {
+		void vscode.window.showInformationMessage(
+			selected.length ? `Tags: ${selected.join(", ")}` : "Tags cleared",
+		);
+	}
+}
+
+/** Add unknown task tags into the task-folder config.yml. */
+export async function runAddTagToProject(
+	deps: FrontmatterEditDeps,
+	uriArg?: string,
+): Promise<void> {
+	const document = await resolveDocument(uriArg);
+	if (!document) {
+		void vscode.window.showErrorMessage(
+			`Open a ${TASK_FILE_EXTENSION} task file first`,
+		);
+		return;
+	}
+
+	const folder = await resolveTaskFolder(document, deps.config);
+	if (!folder) {
+		void vscode.window.showErrorMessage(
+			"Task file is outside a configured task folder",
+		);
+		return;
+	}
+
+	const loaded = await loadProjectConfig(deps.fs, folder);
+	if (loaded.isErr()) {
+		presentError(loaded.error);
+		return;
+	}
+
+	const known = new Set(loaded.value.config.tags);
+	const current = parseTaskTags(document.getText());
+	const unknown = current.filter((tag) => !known.has(tag));
+
+	if (unknown.length === 0) {
+		void vscode.window.showInformationMessage(
+			"All task tags are already in project config",
+		);
+		return;
+	}
+
+	const picked = await vscode.window.showQuickPick(
+		unknown.map((tag) => ({
+			label: tag,
+			tag,
+			picked: true,
+		})),
+		{
+			canPickMany: true,
+			placeHolder: "Add to project config",
+		},
+	);
+	if (!picked || picked.length === 0) return;
+
+	for (const item of picked) {
+		const result = await addProjectTag(deps.fs, {
+			folderPath: folder,
+			tag: item.tag,
+		});
+		if (result.isErr()) {
+			presentError(result.error);
+			return;
+		}
+	}
+
+	void vscode.window.showInformationMessage(
+		`Added to project config: ${picked.map((p) => p.tag).join(", ")}`,
+	);
 }

src/ui/getGitUserName.ts

@@ -21,14 +21,4 @@ export async function getGitUserName(
 	}
 }
 
-/** Quote a YAML scalar for a single-line frontmatter value. */
+export { yamlInlineScalar } from "@/utils/yamlScalar";
-export function yamlInlineScalar(value: string): string {
-	if (value === "") {
-		return '""';
-	}
-	// Safe unquoted token (no spaces / special YAML chars).
-	if (/^[A-Za-z0-9_./+-]+$/.test(value)) {
-		return value;
-	}
-	return JSON.stringify(value);
-}

src/ui/resolveTaskFolder.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import { TaskScope } from "@/model/taskLocation";
+import { resolveTaskFolderForPath } from "./resolveTaskFolder";
+
+describe("resolveTaskFolderForPath", () => {
+	const locations = [
+		{ scope: TaskScope.PROJECT, folderPath: "/ws/.xflow" },
+		{ scope: TaskScope.GLOBAL, folderPath: "/global/tasks" },
+	];
+
+	it("matches project task file", () => {
+		expect(
+			resolveTaskFolderForPath("/ws/.xflow/fix-login.xflow.md", locations),
+		).toBe("/ws/.xflow");
+	});
+
+	it("matches global task file", () => {
+		expect(
+			resolveTaskFolderForPath("/global/tasks/note.xflow.md", locations),
+		).toBe("/global/tasks");
+	});
+
+	it("returns undefined outside task folders", () => {
+		expect(resolveTaskFolderForPath("/ws/src/app.ts", locations)).toBe(
+			undefined,
+		);
+	});
+
+	it("prefers longer matching prefix", () => {
+		const nested = [
+			{ scope: TaskScope.PROJECT, folderPath: "/ws" },
+			{ scope: TaskScope.GLOBAL, folderPath: "/ws/.xflow" },
+		];
+		expect(
+			resolveTaskFolderForPath("/ws/.xflow/a.xflow.md", nested),
+		).toBe("/ws/.xflow");
+	});
+});

src/ui/resolveTaskFolder.ts

@@ -0,0 +1,29 @@
+import * as path from "path";
+import { TaskLocation } from "@/model/taskLocation";
+
+/**
+ * Find the task folder (project/global path) that contains `filePath`.
+ * Longest matching prefix wins.
+ */
+export function resolveTaskFolderForPath(
+	filePath: string,
+	locations: TaskLocation[],
+): string | undefined {
+	const normalized = path.resolve(filePath).replace(/\\/g, "/");
+	let best: string | undefined;
+	let bestLen = -1;
+
+	for (const location of locations) {
+		const folder = path.resolve(location.folderPath).replace(/\\/g, "/");
+		const prefix = folder.endsWith("/") ? folder : `${folder}/`;
+		if (
+			(normalized === folder || normalized.startsWith(prefix)) &&
+			folder.length > bestLen
+		) {
+			best = location.folderPath;
+			bestLen = folder.length;
+		}
+	}
+
+	return best;
+}

src/ui/taskCommands.ts

@@ -11,8 +11,10 @@ import { TaskDashboardPanel } from "@/views/taskDashboardPanel";
 import { TaskKanbanPanel } from "@/views/taskKanbanPanel";
 import { TaskTreeProvider } from "@/views/taskTreeProvider";
 import {
+	runAddTagToProject,
 	runEditTaskPriority,
 	runEditTaskStatus,
+	runEditTaskTags,
 	runSetAssigneeMe,
 } from "./editFrontmatterField";
 import { presentError } from "./presentError";
@@ -27,6 +29,7 @@ export type TaskCommandDeps = {
 	repo: ITaskRepository;
 	config: IConfigProvider;
 	tree: TaskTreeProvider;
+	fs: import("@/ports").IFileSystem;
 	/** Refresh dashboard (and any other listeners) after task mutations. */
 	onTasksMutated?: () => void;
 };
@@ -257,6 +260,16 @@ export function registerTaskCommands(
 			"xboctukFlow.setAssigneeMe",
 			(uri?: string) => runSetAssigneeMe(uri),
 		),
+		vscode.commands.registerCommand(
+			"xboctukFlow.editTaskTags",
+			(uri?: string) =>
+				runEditTaskTags({ fs: deps.fs, config: deps.config }, uri),
+		),
+		vscode.commands.registerCommand(
+			"xboctukFlow.addTagToProject",
+			(uri?: string) =>
+				runAddTagToProject({ fs: deps.fs, config: deps.config }, uri),
+		),
 		vscode.commands.registerCommand("xboctukFlow.openDashboard", () =>
 			runOpenDashboard(deps),
 		),

src/ui/taskDecorations.ts

@@ -42,6 +42,19 @@ function hoverAssigneeMe(document: vscode.TextDocument): vscode.MarkdownString {
 	return md;
 }
 
+function hoverTags(document: vscode.TextDocument): vscode.MarkdownString {
+	const uri = document.uri.toString();
+	const md = new vscode.MarkdownString(
+		[
+			`[$(edit) Edit tags…](${commandUri("xboctukFlow.editTaskTags", [uri])})`,
+			`[$(repo-push) Add tag to project](${commandUri("xboctukFlow.addTagToProject", [uri])})`,
+		].join(" · "),
+	);
+	md.isTrusted = true;
+	md.supportThemeIcons = true;
+	return md;
+}
+
 export function registerTaskDecorations(
 	context: vscode.ExtensionContext,
 ): void {
@@ -106,6 +119,25 @@ export function registerTaskDecorations(
 			});
 		}
 
+		const tagsRange = findFieldRange(text, EditableField.TAGS);
+		if (tagsRange) {
+			options.push({
+				range: new vscode.Range(
+					tagsRange.startLine,
+					tagsRange.startCol,
+					tagsRange.endLine,
+					tagsRange.endCol,
+				),
+				hoverMessage: hoverTags(editor.document),
+				renderOptions: {
+					after: {
+						contentText: " ✎ tags",
+						color: new vscode.ThemeColor("textLink.foreground"),
+					},
+				},
+			});
+		}
+
 		editor.setDecorations(decorationType, options);
 	};
 

src/ui/taskDiagnostics.ts

@@ -1,12 +1,22 @@
 import * as vscode from "vscode";
+import { resolveTaskLocations } from "@/commands/resolveTaskLocations";
+import { loadProjectConfig } from "@/commands/loadProjectConfig";
 import {
 	validateFrontmatter,
 	type FrontmatterIssue,
 } from "@/frontmatter/validateFrontmatter";
+import { TASK_FOLDER_CONFIG_FILENAME } from "@/model/projectConfig";
 import { isTaskFileName, TASK_LANGUAGE_ID } from "@/model/taskFile";
+import { IConfigProvider, IFileSystem } from "@/ports";
+import { resolveTaskFolderForPath } from "./resolveTaskFolder";
 
 const DEBOUNCE_MS = 200;
 
+export type TaskDiagnosticsDeps = {
+	fs: IFileSystem;
+	config: IConfigProvider;
+};
+
 function isTaskDocument(document: vscode.TextDocument): boolean {
 	if (document.uri.scheme !== "file" && document.uri.scheme !== "untitled") {
 		return false;
@@ -45,19 +55,46 @@ function toDiagnostic(issue: FrontmatterIssue): vscode.Diagnostic {
 
 export function registerTaskDiagnostics(
 	context: vscode.ExtensionContext,
+	deps: TaskDiagnosticsDeps,
 ): vscode.DiagnosticCollection {
 	const collection =
 		vscode.languages.createDiagnosticCollection("xboctuk-flow");
 	context.subscriptions.push(collection);
 
 	const timers = new Map<string, ReturnType<typeof setTimeout>>();
+	/** folderPath → knownTags when config exists; undefined key means skip catalog. */
+	const knownTagsByFolder = new Map<string, string[] | undefined>();
 
-	const lint = (document: vscode.TextDocument): void => {
+	const invalidateFolder = (folderPath: string): void => {
+		knownTagsByFolder.delete(folderPath);
+	};
+
+	const getKnownTags = async (
+		folderPath: string | undefined,
+	): Promise<string[] | undefined> => {
+		if (!folderPath) return undefined;
+		if (knownTagsByFolder.has(folderPath)) {
+			return knownTagsByFolder.get(folderPath);
+		}
+		const loaded = await loadProjectConfig(deps.fs, folderPath);
+		if (loaded.isErr() || !loaded.value.exists) {
+			knownTagsByFolder.set(folderPath, undefined);
+			return undefined;
+		}
+		knownTagsByFolder.set(folderPath, loaded.value.config.tags);
+		return loaded.value.config.tags;
+	};
+
+	const lint = async (document: vscode.TextDocument): Promise<void> => {
 		if (!isTaskDocument(document)) {
 			collection.delete(document.uri);
 			return;
 		}
-		const issues = validateFrontmatter(document.getText());
+
+		const locations = resolveTaskLocations(deps.config);
+		const folder = resolveTaskFolderForPath(document.fileName, locations);
+		const knownTags = await getKnownTags(folder);
+		const issues = validateFrontmatter(document.getText(), { knownTags });
 		collection.set(document.uri, issues.map(toDiagnostic));
 	};
 
@@ -69,17 +106,43 @@ export function registerTaskDiagnostics(
 			key,
 			setTimeout(() => {
 				timers.delete(key);
-				lint(document);
+				void lint(document);
 			}, DEBOUNCE_MS),
 		);
 	};
 
+	const relintAllTasks = (): void => {
+		for (const document of vscode.workspace.textDocuments) {
+			if (isTaskDocument(document)) {
+				void lint(document);
+			}
+		}
+	};
+
 	for (const document of vscode.workspace.textDocuments) {
-		lint(document);
+		void lint(document);
+	}
+
+	for (const location of resolveTaskLocations(deps.config)) {
+		const configPattern = new vscode.RelativePattern(
+			location.folderPath,
+			TASK_FOLDER_CONFIG_FILENAME,
+		);
+		const watcher = vscode.workspace.createFileSystemWatcher(configPattern);
+		const onConfigChange = (): void => {
+			invalidateFolder(location.folderPath);
+			relintAllTasks();
+		};
+		watcher.onDidCreate(onConfigChange);
+		watcher.onDidChange(onConfigChange);
+		watcher.onDidDelete(onConfigChange);
+		context.subscriptions.push(watcher);
 	}
 
 	context.subscriptions.push(
-		vscode.workspace.onDidOpenTextDocument(lint),
+		vscode.workspace.onDidOpenTextDocument((doc) => {
+			void lint(doc);
+		}),
 		vscode.workspace.onDidChangeTextDocument((event) => {
 			lintDebounced(event.document);
 		}),

src/utils/yamlScalar.ts

@@ -0,0 +1,11 @@
+/** Quote a YAML scalar for a single-line frontmatter value. */
+export function yamlInlineScalar(value: string): string {
+	if (value === "") {
+		return '""';
+	}
+	// Safe unquoted token (no spaces / special YAML chars).
+	if (/^[A-Za-z0-9_./+-]+$/.test(value)) {
+		return value;
+	}
+	return JSON.stringify(value);
+}