[Refactor] Extract a shared helper for dynamic-route path joining (root-base slash normalization)

[MelvinBot]

Problem

The logic that joins a dynamic-route base path with its suffix — special-casing a root base (/) so the two aren't concatenated into a //-prefixed (protocol-relative) path — is duplicated in several places in the navigation layer:

• src/libs/Navigation/helpers/getPathFromState.ts:170
• src/libs/Navigation/helpers/getPathFromState.ts:144
• src/libs/Navigation/helpers/dynamicRoutesUtils/createDynamicRoute.ts:53

Each site independently does base === '/' ? \/${suffix}` : `${base}/${suffix}`. Because this same rule lives in multiple places, it's easy for one copy to drift or be forgotten — which is exactly what caused the SecurityError: Failed to execute 'pushState'crash fixed in Expensify/App#97849 (thegetPathFromStatecopy was missing the root-base guard and produced//ai-features-promo`).

Proposed change

Extract a small shared helper (e.g. joinPathSegments(base, suffix)) that returns the correctly-adjusted path, and use it at every site above so the slash-normalization rule is defined once.

Note

This came out of a NAB review comment on the fix PR: #97849 (comment)

NAB: Maybe we can extract a helper to return an adjusted path. I see that this logic is repeated elsewhere in the code

Follow-up to #97849.

Issue Owner

Current Issue Owner: @collectioneur

[melvin-bot]

This issue has not been updated in over 15 days. @mountiny, @collectioneur eroding to Monthly issue.

P.S. Is everyone reading this sure this is really a near-term priority? Be brave: if you disagree, go ahead and close it out. If someone disagrees, they'll reopen it, and if they don't: one less thing to do!

[mountiny]

@collectioneur Are you able to follow up on this one?

[collectioneur]

Sure, I'll prepare a PR for this. Missed that!

[collectioneur]

Opened the PR