fix(billing): correct URL construction and prevent double-redirecting

[jonathanlab]

TL;DR

Fixes a critical billing navigation bug where the billing link was constructing malformed URLs with double schemes (e.g., https://us.posthog.com/project/219767/https://app.posthog.com/organization/billing), resulting in 404 errors. Introduces a dedicated getBillingUrl() function to ensure consistent, correct billing URL construction across the application.

What changed?

• Added getBillingUrl() function in urls.ts that constructs the correct billing URL (/organization/billing/overview) with proper region handling
• Fixed billing URL construction in PlanUsageSettings.tsx:
  • Replaced getPostHogUrl("/organization/billing") with getBillingUrl()
  • Fixed redirect URL logic to use the billing URL directly instead of attempting to construct a separate redirect URL that was causing double-scheme concatenation
• Added comprehensive test coverage in urls.test.ts to prevent regression:
  • Tests for getPostHogUrl() behavior with different regions
  • Tests for getBillingUrl() returning correct URLs for US and EU regions
  • Explicit test case verifying the malformed double-scheme URL is no longer produced

How did you test this?

The changes include new unit tests in urls.test.ts that verify:

• Correct URL construction for both US and EU regions
• Proper handling of missing regions (returns null)
• Prevention of malformed double-scheme URLs
• No accidental inclusion of /project/ paths in billing URLs

---

Created with PostHog Code

[greptile-apps]

Prompt To Fix All With AI

Fix the following 3 code review issues. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 3
apps/code/src/renderer/utils/urls.test.ts:14-24
The region-specific test cases for both `getPostHogUrl` and `getBillingUrl` are repetitive and should be expressed as parameterised tests — the team's stated preference. Duplicate test bodies hide whether the assertion is actually exercising distinct behaviour or just paraphrasing the same check with different literals.

```suggestion
  it.each([
    ["us", "/foo", "https://us.posthog.com/foo"],
    ["us", "foo", "https://us.posthog.com/foo"],
    ["eu", "/foo", "https://eu.posthog.com/foo"],
  ])("joins base and path for %s region (path=%s)", (region, path, expected) => {
    expect(getPostHogUrl(path, region as "us" | "eu")).toBe(expected);
  });
```

### Issue 2 of 3
apps/code/src/renderer/utils/urls.test.ts:28-38
Same parameterisation opportunity for the `getBillingUrl` region cases — the two "points at" tests differ only in region and expected host, making `it.each` the right tool.

```suggestion
  it.each([
    ["us", "https://us.posthog.com/organization/billing/overview"],
    ["eu", "https://eu.posthog.com/organization/billing/overview"],
  ])("points at /organization/billing/overview on %s", (region, expected) => {
    expect(getBillingUrl(region as "us" | "eu")).toBe(expected);
  });
```

### Issue 3 of 3
apps/code/src/renderer/features/settings/components/sections/PlanUsageSettings.tsx:71
**`redirectUrl` value is silently discarded**

The old code passed `redirectUrl` to `getPostHogUrl()` as the path — that was broken when the backend returned a full URL. The new code fixes the double-scheme issue, but now completely ignores the backend-supplied URL: `redirectUrl` only controls whether the callout is shown; its actual value is thrown away. If the backend ever sends a redirect to a specific checkout or payment-setup page (rather than the generic billing overview), users will silently land on the wrong page.

```suggestion
  const redirectFullUrl = redirectUrl ? billingUrl : null;
```

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