chore(pass-style): only Promise<Passable> is passable

[michaelfig]

Description

This PR strengthens TypeScript type safety for passable promises by requiring them to accept only Promise<Passable> rather than Promise<any>. This prevents promises that will likely fulfill to non-passable values from being accepted at compile time.

Changes:

• Added AwaitedPassable type, which only includes the non-Promise branches of the existing Passable union type.
• Updated Passable type to be AwaitedPassable | Promise<AwaitedPassable> to break infinite promise expansion.
• Simplified PassByRef type to use a single Promise<Passable> instead of multiple specific promise types
• Added AwaitedPassableCap type, which only includes the non-Promise branches of the existing PassableCap union type.
• Updated PassableCap type to be AwaitedPassableCap | Promise<Passable> instead of ... | Promise<any>.
• Added test annotations to validate the new type constraints

Security Considerations

Guardrails only. By design, the TypeScript programming language provides pragmatic but unsound types.

Scaling Considerations

n/a

Documentation Considerations

Documented in NEWS.md, but should be intuitive enough, and can always be @ts-expect-errorred if it gets in the way.

Testing Considerations

CI, and types.test-d.ts linting.

Compatibility Considerations

Should not break naïve code, only code that is really doing something dodgy.

Upgrade Considerations

Types only. No effect on runtime execution.

[Copilot]

Pull request overview

This PR strengthens TypeScript type safety for passable promises by constraining them to only accept Promise<Passable> instead of Promise<any>. This prevents promises that will likely fulfill to non-passable values from being accepted at compile time.

Changes:

• Updated type definitions to require promises to be Promise<Passable> instead of Promise<any>
• Simplified PassByRef type to use a single Promise<Passable> instead of multiple specific promise types
• Made AwaitedPassableCap an internal type since it's only used within the type definitions
• Added test annotations to validate the new type constraints

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
packages/pass-style/src/types.d.ts	Tightened promise types from Promise<any> to Promise<Passable> across PassByRef, PassStyleOf, and PassableCap; made AwaitedPassableCap internal
packages/pass-style/src/types.test-d.ts	Added @ts-expect-error annotations to verify promises of non-passable values are correctly rejected by the type system
packages/pass-style/NEWS.md	Documented the type changes and their purpose

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[mhofman]

I have tried to do this before (taking over an attempt from @turadg), and things broke horribly in agoric-sdk (Agoric/agoric-sdk#9943)

[turadg]

I'd love to see this tightened up. But per what Mathieu pointed out, I'm requesting that the test plan include a green integration branch with agoric-sdk. (IMO that can use ts-expect-error and other escape hatches so we can correct Endo and catch in in agoric-sdk over time.)