feat(shared): add unified DeepLinkResolver with polymorphic fallback chain

[Itzzavdheshh]

Summary

Closes #42

This PR introduces a unified DeepLinkResolver utility in packages/shared that eliminates fragmented deep-link logic previously spread across platforms.ts and the backend follow.ts route. The resolver implements a polymorphic fallback chain — native-deeplink → universal-link → web-url → webview — and is consumed by both the mobile screen and the backend API, removing all duplicated URL construction logic.

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Type of Change

• Bug fix
• New feature
• Refactor (no functional change)
• UI / Design change
• Tests only
• Documentation
• Infrastructure / DevOps
• Security

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What Changed

• packages/shared/src/deepLinks.ts (new): defines LinkStrategy, ResolvedLink types and exports resolveDeepLink(platform, username, context) which builds and returns the full priority fallback chain based on device + app-install context.
• packages/shared/src/platforms.ts: extends PlatformDef interface with nativeScheme: string | null, universalLink: string | null, and webViewFallback: boolean; updates all 17 platform registry entries with correct values.
• packages/shared/src/index.ts: re-exports everything from ./deepLinks so consumers import from @devcard/shared.
• apps/backend/src/routes/follow.ts: replaces ad-hoc URL assembly with a call to resolveDeepLink(..., { isMobile: false }); returns { strategy: 'webview', url } when the resolved strategy is webview.
• apps/mobile/src/screens/DevCardViewScreen.tsx: introduces executeResolvedLinkChain(resolved, link) async helper; refactors handlePlatformAction for all three action variants to call resolveDeepLink and traverse the chain with Linking.canOpenURL / Linking.openURL, falling back to handleWebViewConnect when strategy === 'webview'.
• packages/shared/src/__tests__/deepLinks.test.ts (new): Vitest suite covering all 4 strategies, full chain traversal in mobile + desktop context, and {username} interpolation for all platforms.

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How to Test

1. Run TypeScript type-check in the shared package:
   pnpm --filter @devcard/shared typecheck
2. Run the new unit tests in isolation:
   pnpm --filter @devcard/shared test src/__tests__/deepLinks.test.ts
3. Run the backend follow endpoint tests:
   pnpm --filter @devcard/backend test src/__tests__/follow.test.ts
4. Run the full test suite to confirm no regressions:
   pnpm -r test
5. On a physical device (or simulator) with LinkedIn installed, tap the LinkedIn connect button — verify the app opens directly. Remove LinkedIn and tap again — verify the in-app webview fallback is used.

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Checklist

• My code follows the project's coding style (pnpm -r run lint passes).
• TypeScript compiles without errors (pnpm -r run typecheck).
• I have added or updated tests for the changes I made.
• All tests pass locally (pnpm -r run test).
• I have updated documentation where necessary.
• No new console.log or debug statements left in the code.
• Breaking changes are documented in this PR description.

Breaking changes: The PlatformDef interface now requires three new fields (nativeScheme, universalLink, webViewFallback). Any downstream code that constructs a PlatformDef object manually must be updated to include these fields. All 17 entries in PLATFORMS have been updated; no runtime breakage is expected.

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Screenshots / Recordings

Not applicable — no UI changes; behaviour is functionally equivalent with improved reliability.

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Additional Context

• The fallback chain is intentionally lazy: each node holds an optional .fallback reference rather than a flat array, making it easy to extend with new strategies in the future without breaking existing consumers.
• webViewFallback: true is currently set only for LinkedIn and Twitter/X, which require authenticated sessions that prevent direct in-app browsing.
• Future work: consider caching the result of Linking.canOpenURL per platform per session to avoid repeated async checks on repeated taps.

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Submitted as part of Open Source Contribution — GSSoC (GirlScript Summer of Code)

[Itzzavdheshh]

Hi @ShantKhatri & @Harxhit — thanks for taking the time to review this!

Unified Deep-Link Resolver — cross-package refactor

Introduced a shared resolveDeepLink utility in packages/shared that consolidates
all platform URL logic into a single, typed, polymorphic fallback chain
(native-deeplink → universal-link → web-url → webview).

Previously, deep-link construction was duplicated across the backend follow route
and the mobile DevCardViewScreen, each with its own branching logic and no shared
contract. This change gives every current and future platform a first-class resolver
entry (nativeScheme, universalLink, webViewFallback) and makes both consumers
— mobile and backend — delegate entirely to the shared package.

Difficulty: senior | Scope: packages/shared, apps/backend, apps/mobile
Tests added: exhaustive Vitest suite covering all 4 strategies and all 17 platforms.

Happy to address any feedback or make adjustments — just let me know! 🚀

[Itzzavdheshh]

Hi @ShantKhatri updates?

[vercel]

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[github-actions]

CI — All Checks Passed

Backend — PASS

Check	Result
Lint	PASS
Test	PASS
Typecheck	PASS

Mobile — PASS

Check	Result
Lint	PASS
Test	PASS

Web — PASS

Check	Result
Check	PASS
Build	PASS

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Last updated: Sat, 06 Jun 2026 12:26:14 GMT

[Itzzavdheshh]

Hi @ShantKhatri please check , i did some changes ...i request you to please review and give necessary feedback and i am happy to address them . Thanku

[Itzzavdheshh]

Hi @ShantKhatri are you closing this one too?

[Itzzavdheshh]

@ShantKhatri ???

[ShantKhatri]

Hi @ShantKhatri are you closing this one too?

Yes

[Itzzavdheshh]

@ShantKhatri bro i spend so much time and make so much effort on this one , and it all goes to recycle bin 😢

[ShantKhatri]

@ShantKhatri bro i spend so much time and make so much effort on this one , and it all goes to recycle bin 😢

But this PR was not supposed to be reviewed, as it's recommended to have short reviewable PR. This PR had about 45 files changed and was flooded with features.