refactor(shared): extract task contracts and model policy

[richardsolomou]

Problem

Desktop task contracts and model policy were tied to agent-specific modules, preventing other hosts from reusing them without duplicating behavior. Two current-main UI tests also asserted before asynchronous tab and Markdown content mounted under CI load.

Refs PostHog/posthog#76229

Changes

Phase 1 only: I moved the existing desktop contracts and model policy into @posthog/shared. Mobile remains unchanged. The UI test changes only wait for rendered behavior and do not change product behavior.

How did you test this?

• Full monorepo typecheck
• Full UI suite: 2,113 tests
• Full mobile suite: 451 tests
• Repeated the two CI-racing UI tests 10 times

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit b4e9084.}

[jonathanlab]

shared can be used for exporting contract types, but now we're also moving a ton of logic in to there, which should move to core.

The aim is to make core a reusable set of logic by different surfaces, web, mobile, desktop, which does not rely on any platform dependencies. If we move too much logic into shared it risks becoming this unstructured dependency layer, which can bypass all the strict architectural boundaries we're enforcing around core.

[richardsolomou]

• feat(mobile): add Codex task parity #3654
• refactor(mobile): finalize portability boundary #3642
• refactor(mobile): adopt shared interaction semantics #3641
• refactor(mobile): finish shared task and inbox adoption #3640
• refactor(mobile): adopt shared task runtime #3637
• refactor(core): extract shared presentation semantics #3635
• refactor(core): extract permission and composer semantics #3634
• refactor(core): extract repository integration semantics #3633
• refactor(core): extract portable cloud task engine #3608
• refactor(core): rename cloud task service as engine #3624
• refactor(core): extract cloud task policies #3623
• refactor(api-client): extract cloud task transport #3622
• refactor(shared): extract task contracts and model policy #3616 👈 (View in Graphite)
• main

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[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
apps/mobile/src/features/tasks/composer/options.ts:84-89
**Reasoning options ignore selected model**

When a user selects Claude Sonnet 4.6, the picker still exposes the Opus-derived `xhigh` and `max` levels, and the selected value is sent directly in the run payload or `set_config_option` command. Shared policy supports only `low`, `medium`, and `high` for Sonnet 4.6, so these selections produce an unsupported configuration that is rejected or misapplied.

_{Reviews (1): Last reviewed commit: "Merge main into shared task foundations" | Re-trigger Greptile}

[richardsolomou]

moved the composer policy into core in #3637, so shared is back to contracts and primitives.

[trunk-io]

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