feat(tags): pure Tag draft validation/normalisation (TDD)

validateTagDraft: trims + requires a name, caps it at 30 chars, rejects a
case-insensitive duplicate against the portfolio's existing tag names (the
caller excludes the tag's own name on edit), and validates + lowercases a
freeform hex colour (#rgb or #rrggbb). The DB's case-insensitive unique index
remains the ultimate guard; this gives a friendly pre-check for the tag routes
and settings UI. 8 behaviours, built red-green. ADR-0013.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/tags/model.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from "vitest";
+import { validateTagDraft } from "./model";
+
+describe("validateTagDraft", () => {
+  it("accepts a valid name + hex colour, trimming the name and lowercasing the hex", () => {
+    expect(validateTagDraft({ name: "  Void  ", colour: "#7C3AED" }, [])).toEqual({
+      ok: true,
+      tag: { name: "Void", colour: "#7c3aed" },
+    });
+  });
+
+  it("rejects a blank name (empty or whitespace-only)", () => {
+    expect(validateTagDraft({ name: "   ", colour: "#7c3aed" }, [])).toEqual({
+      ok: false,
+      error: "Tag name is required",
+    });
+  });
+
+  it("rejects a name longer than 30 characters (after trimming)", () => {
+    const long = "a".repeat(31);
+    expect(validateTagDraft({ name: long, colour: "#7c3aed" }, [])).toEqual({
+      ok: false,
+      error: "Tag name must be 30 characters or fewer",
+    });
+  });
+
+  it("accepts a name of exactly 30 characters (boundary)", () => {
+    const name = "a".repeat(30);
+    expect(validateTagDraft({ name, colour: "#7c3aed" }, [])).toEqual({
+      ok: true,
+      tag: { name, colour: "#7c3aed" },
+    });
+  });
+
+  it("rejects a name that duplicates an existing one, case-insensitively", () => {
+    expect(
+      validateTagDraft({ name: "  VOID ", colour: "#7c3aed" }, ["Void", "Phase 1"]),
+    ).toEqual({ ok: false, error: "A tag with this name already exists" });
+  });
+
+  it("accepts a name that clashes with no existing tag (edit excludes its own name)", () => {
+    // On edit the caller passes the OTHER tags' names, so keeping/​recasing the
+    // tag's own name is allowed.
+    expect(
+      validateTagDraft({ name: "Void", colour: "#7c3aed" }, ["Phase 1"]),
+    ).toEqual({ ok: true, tag: { name: "Void", colour: "#7c3aed" } });
+  });
+
+  it("rejects a colour that is not a hex code", () => {
+    expect(validateTagDraft({ name: "Void", colour: "red" }, [])).toEqual({
+      ok: false,
+      error: "Colour must be a hex code like #7c3aed",
+    });
+  });
+
+  it("accepts a 3-digit hex shorthand, normalised to lowercase", () => {
+    expect(validateTagDraft({ name: "Void", colour: "#ABC" }, [])).toEqual({
+      ok: true,
+      tag: { name: "Void", colour: "#abc" },
+    });
+  });
+});

src/lib/tags/model.ts

@@ -0,0 +1,43 @@
+/**
+ * Pure Tag domain logic — validation + normalisation for creating/editing a
+ * portfolio Tag (ADR-0013). Kept free of DB access so it unit-tests cleanly and
+ * is shared by the tag routes. The DB's case-insensitive unique index is the
+ * ultimate guard against duplicate names; this gives a friendly pre-check.
+ */
+
+export const MAX_TAG_NAME_LENGTH = 30;
+
+/** A hex colour: #rgb or #rrggbb (case-insensitive). */
+const HEX_COLOUR = /^#([0-9a-f]{3}|[0-9a-f]{6})$/i;
+
+export interface TagDraft {
+  name: string;
+  colour: string;
+}
+
+export type TagValidation =
+  | { ok: true; tag: TagDraft }
+  | { ok: false; error: string };
+
+export function validateTagDraft(
+  input: TagDraft,
+  existingNames: string[],
+): TagValidation {
+  const name = input.name.trim();
+  if (name.length === 0) return { ok: false, error: "Tag name is required" };
+  if (name.length > MAX_TAG_NAME_LENGTH) {
+    return {
+      ok: false,
+      error: `Tag name must be ${MAX_TAG_NAME_LENGTH} characters or fewer`,
+    };
+  }
+  const lower = name.toLowerCase();
+  if (existingNames.some((existing) => existing.trim().toLowerCase() === lower)) {
+    return { ok: false, error: "A tag with this name already exists" };
+  }
+  const colour = input.colour.trim().toLowerCase();
+  if (!HEX_COLOUR.test(colour)) {
+    return { ok: false, error: "Colour must be a hex code like #7c3aed" };
+  }
+  return { ok: true, tag: { name, colour } };
+}