[codex] Add Carbon fallback for CLI ads

[brandonkachen]

Summary

• add fallbackProvider support to useGravityAd so the CLI retries a secondary ad network when the primary returns no fill or errors
• switch chat ads and the freebuff waiting room to try Gravity first and fall back to Carbon
• keep the existing banner/choice rendering and rotation behavior while broadening fill coverage

Validation

• bun x tsc --noEmit -p cli/tsconfig.json

[greptile-apps]

Greptile Summary

Adds a fallbackProvider option to useGravityAd so the CLI sequentially tries a secondary ad network when the primary returns no fill or an HTTP error. Both call-sites (chat.tsx and waiting-room-screen.tsx) are updated to use Gravity as primary and Carbon as fallback.

Confidence Score: 5/5

Safe to merge — fallback logic is correct, dependency array is properly updated, and all remaining comments are P2 style suggestions.

The core retry loop correctly uses continue on HTTP errors and implicit fall-through on no-fill, both of which advance to the fallback provider. The useEffect dependency array now includes provider and fallbackProvider, so the interval resets properly if they ever change. No correctness issues were found; only minor observability and style suggestions remain.

No files require special attention.

Important Files Changed

Filename	Overview
cli/src/hooks/use-gravity-ad.ts	Adds fallbackProvider param; wraps single fetch in a for-loop over [provider, fallbackProvider]; adds both to the useEffect dependency array. Logic is correct — continue on HTTP error and implicit fall-through on no-fill both advance to the fallback provider.
cli/src/chat.tsx	Adds provider: 'gravity' and fallbackProvider: 'carbon' to the existing useGravityAd call; no other logic changes.
cli/src/components/waiting-room-screen.tsx	Switches waiting-room from Carbon-only (provider: 'carbon') to Gravity-first with Carbon fallback; comment updated to match.

Prompt To Fix All With AI

This is a comment left during a code review.
Path: cli/src/hooks/use-gravity-ad.ts
Line: 284-287

Comment:
**Simplify `providersToTry` construction**

The dedup check (`fallbackProvider !== provider`) can be collapsed using `Set`, which also handles the `undefined` case more naturally without the extra boolean guard:

```suggestion
    const providersToTry = [...new Set([provider, fallbackProvider].filter((p): p is AdProvider => p != null))]
```

This removes the nested ternary and makes the intent ("unique, defined providers in priority order") immediately clear.

How can I resolve this? If you propose a fix, please make it concise.

---

This is a comment left during a code review.
Path: cli/src/hooks/use-gravity-ad.ts
Line: 309-319

Comment:
**Silent no-fill fallback makes debugging harder**

When the primary provider returns a 200 with no ad content (neither `data.ad` nor a valid `data.ads` array), the loop falls through to the fallback silently — no log line is emitted. Adding a brief `logger.debug` here would make it easy to spot "primary returned no fill, trying fallback" in logs without changing behaviour:

```suggestion
        if (data.ad) {
          return { variant: 'banner', ad: data.ad as AdResponse }
        }

        // No fill from this provider; try the next one if available
        logger.debug({ provider: providerToTry }, '[ads] No fill, trying next provider')
```

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "Add Carbon fallback for ads" | Re-trigger Greptile}

[greptile-apps]

Simplify providersToTry construction

The dedup check (fallbackProvider !== provider) can be collapsed using Set, which also handles the undefined case more naturally without the extra boolean guard:

Suggested change

	const providersToTry =
	fallbackProvider && fallbackProvider !== provider
	? [provider, fallbackProvider]
	: [provider]
	const providersToTry = [...new Set([provider, fallbackProvider].filter((p): p is AdProvider => p != null))]

This removes the nested ternary and makes the intent ("unique, defined providers in priority order") immediately clear.

Prompt To Fix With AI

This is a comment left during a code review.
Path: cli/src/hooks/use-gravity-ad.ts
Line: 284-287

Comment:
**Simplify `providersToTry` construction**

The dedup check (`fallbackProvider !== provider`) can be collapsed using `Set`, which also handles the `undefined` case more naturally without the extra boolean guard:

```suggestion
    const providersToTry = [...new Set([provider, fallbackProvider].filter((p): p is AdProvider => p != null))]
```

This removes the nested ternary and makes the intent ("unique, defined providers in priority order") immediately clear.

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[greptile-apps]

Silent no-fill fallback makes debugging harder

When the primary provider returns a 200 with no ad content (neither data.ad nor a valid data.ads array), the loop falls through to the fallback silently — no log line is emitted. Adding a brief logger.debug here would make it easy to spot "primary returned no fill, trying fallback" in logs without changing behaviour:

Suggested change

	if (!response.ok) {
	logger.warn(
	{
	provider: providerToTry,
	status: response.status,
	response: await response.json(),
	},
	'[ads] Web API returned error',
	)
	continue
	}
	if (data.ad) {
	return { variant: 'banner', ad: data.ad as AdResponse }
	}
	// No fill from this provider; try the next one if available
	logger.debug({ provider: providerToTry }, '[ads] No fill, trying next provider')

Prompt To Fix With AI

This is a comment left during a code review.
Path: cli/src/hooks/use-gravity-ad.ts
Line: 309-319

Comment:
**Silent no-fill fallback makes debugging harder**

When the primary provider returns a 200 with no ad content (neither `data.ad` nor a valid `data.ads` array), the loop falls through to the fallback silently — no log line is emitted. Adding a brief `logger.debug` here would make it easy to spot "primary returned no fill, trying fallback" in logs without changing behaviour:

```suggestion
        if (data.ad) {
          return { variant: 'banner', ad: data.ad as AdResponse }
        }

        // No fill from this provider; try the next one if available
        logger.debug({ provider: providerToTry }, '[ads] No fill, trying next provider')
```

How can I resolve this? If you propose a fix, please make it concise.