fix(rollup-plugin): use stable chunk ids in symbol-set mode

[Cypher-Aura-19]

Problem

The default symbol-set renderChunk path injected a random UUID into each chunk before Rollup calculated [hash] filenames. Because the random ID became part of the emitted content, identical builds produced different chunk hashes and renamed every JS chunk on every build, breaking long-term asset caching and causing Failed to fetch dynamically imported module errors on stale tabs.

Changes

• Use content-derived chunk IDs in symbol-set mode, matching the stable behavior already used by event mode
• Update unit coverage so identical content keeps the same chunk ID and changed content gets a different ID
• Add a Vite regression test verifying identical builds keep identical [hash] filenames
• Add a patch changeset for @posthog/rollup-plugin

Testing

• Rollup-plugin unit tests: 26/26 passing

• Lint on modified rollup-plugin files: passing

• Standalone regression verification confirms:

  • identical content → same chunk ID and hash
  • changed content → different chunk ID and hash
  • reverting the fix restores the failing random-hash behavior

• The Vite functional test cannot run locally on Windows because this repository intentionally installs native bindings only for Linux/macOS; it should run in CI

Closes #4670

Release info Sub-libraries affected

Libraries affected

• @posthog/rollup-plugin

Checklist

• Tests for new code
• Accounted for the impact of any changes across different platforms
• Accounted for backwards compatibility of any changes (no breaking changes!)
• Took care not to unnecessarily increase the bundle size

If releasing new changes

• Ran pnpm changeset to generate a changeset file

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Implemented with Claude Code under human direction and review. The root cause was confirmed in the default symbol-set renderChunk path, the fix is limited to using the existing content-derived chunk-ID helper, and the regression was verified with unit tests and a standalone content-hash check. The Vite functional test was added but could not be executed locally on Windows due to the repository's Linux/macOS-only native binding configuration.

[marandaneto]

cc @PostHog/team-error-tracking i reviewed and fixed an issue, pls double check

[ablaszkiewicz]

@marandaneto we can't use stable chunk ids in symbol set mode because if we do and some chunks are the same across releases, we lose correct release attribution for versions which are still using old chunks. So two things happen here:

• if somebody runs this without any flags (vast majority of people in JS world), you get an error that this chunk already belongs to a different release,
• if somebody uses force flag, we overwrite the release this chunk belongs to to a new one so old versions of the app report exceptions as if they were the newest release.

In event mode we can do this because release is injected into the chunk and attached to the event (and not fetched from the symbol set)

We need to solve this in a different way. I'll think about this.

[ablaszkiewicz]

As per my comment above. Let me see what's up with this and come up with a better solution

[marandaneto]

As per my comment above. Let me see what's up with this and come up with a better solution

thanks for the review and good catch
moving to draft until we know how to solve this