nip55: source the batch cap from keep-mobile via nip55MaxBatchSize()

[wksantiago]

Closes #327.

MAX_BATCH_SIZE = 20 was duplicated in Nip55Activity and keep-mobile's handle_batch_request, kept in sync by hand. This removes the Kotlin copy and reads the cap from keep-mobile's new nip55MaxBatchSize() FFI, making Rust the sole owner of batch policy.

Depends on privkeyio/keep#974 — keep.version is bumped to that keep commit (bd8ca8d). CI will go green once #974 merges and the pin is re-set to the merged SHA if it changes.

Scope

This intentionally does not fold the whole Kotlin batch loop into a Rust entry point (the "proposed fix" in #327). That loop also does per-request preApprove, permission grants, audit, keystore context and the biometric gate — all Android-side — so folding it would require a large new FFI callback surface, i.e. more complexity for a p3 purity item. Single-sourcing the constant resolves the actual duplication without that cost.

Verification

:app:compileDebugKotlin BUILD SUCCESSFUL — :buildRust regenerated the uniffi bindings with nip55MaxBatchSize and Kotlin typechecked against them.

Summary by CodeRabbit

• Bug Fixes
  • Updated batch processing to use the current supported limit, improving compatibility and reliability.
• Chores
  • Updated the application’s internal version reference.

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: ec7ef289-5639-4358-b0d8-f67ebe6461fb

📥 Commits

Reviewing files that changed from the base of the PR and between 39118ed and b18f1cf.

📒 Files selected for processing (2)

• app/src/main/kotlin/io/privkey/keep/nip55/Nip55Activity.kt
• keep.version

Walkthrough

The change updates the pinned keep-mobile implementation and replaces the hardcoded NIP-55 batch limit with nip55MaxBatchSize() in Nip55Activity.

Changes

NIP-55 batch limit integration

Layer / File(s)	Summary
Pinned implementation and batch limit integration keep.version, app/src/main/kotlin/io/privkey/keep/nip55/Nip55Activity.kt	The pinned keep-mobile version changes. Nip55Activity imports nip55MaxBatchSize() and uses its Int value instead of the hardcoded limit 20.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to 39118

This change moves batch-size ownership to the keep-mobile dependency, but the current pin targets a pull-request commit that may become unreachable after squash merging, causing dependency resolution or release builds to fail. The PR is not merge-ready until the pin is updated to the merged commit; the initialization behavior should also be confirmed by the owner.

Suggested reviewers: kwsantiago

Poem

A rabbit checked the batch cap with care,
And found Rust’s number waiting there.
The old hardcode hopped away,
While pinned code joined the play.
NIP-55 now bounds each share.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly states that NIP-55 now sources the batch cap from keep-mobile through nip55MaxBatchSize().
Linked Issues check	✅ Passed	The PR removes the duplicated Kotlin cap and sources it from Rust through nip55MaxBatchSize(), matching issue #327's policy-ownership objective.
Out of Scope Changes check	✅ Passed	The Kotlin change and keep.version update directly support the NIP-55 batch-cap change; no unrelated code changes are shown.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.

✨ Finishing Touches

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• Commit on current branch

🧪 Generate unit tests (beta)

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• Commit unit tests in branch nip55-fold-batch-cap-327

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[kwsantiago]

The Kotlin change is right, and #974 is now merged so the dependency is satisfied. One blocker on the pin before this can land.

Blocker: keep.version points at a commit that is not on keep's main

The pin is bd8ca8d3, which was the head of the nip55-batch-size-ffi-327 branch. #974 was squash-merged, so main got a new commit, 750d8f5, and the branch commit is not part of that history:

$ git merge-base --is-ancestor bd8ca8d3... origin/main && echo YES || echo NOT
NOT on main

$ git ls-remote origin | grep bd8ca8d3
bd8ca8d3945572923e372efd43231caae2e195d9    refs/pull/974/head

It is reachable only through the pull-request ref. That is enough for CI to pass, because setup-keep uses actions/checkout with a raw SHA against the same GitHub remote and PR refs are fetchable there, which is exactly what makes this easy to miss. It is not enough for the release path: a plain clone fetches refs/heads/* and tags, not refs/pull/*, so the F-Droid srclib checkout of $(cat keep.version) would be resolving a SHA that is on no branch. Pull refs are also not a durable pin.

Repinning to the merged commit fixes it, and I verified that rather than just asserting it. With keep.version set to 750d8f5f44304b009ef1c45313999447020dbd9a locally, testDebugUnitTest and lintDebug pass and the generated binding is present:

19862: fun `nip55MaxBatchSize`(): kotlin.UInt {

Worth saying that this is sequencing rather than an authoring mistake: 750d8f5 did not exist when the PR was opened. It just has to be updated now that #974 has landed.

One observation on the Kotlin side

MAX_BATCH_SIZE moves from a const val to private val MAX_BATCH_SIZE = nip55MaxBatchSize().toInt() in the companion, and gate reads it in an instance initializer (:64). So what was a compile-time constant inlined at its use sites is now an FFI call executed when Nip55Activity is first class-loaded, before onCreate.

On the normal path that is fine: Application.onCreate runs initializeKeepMobile() first, so the native library is loaded. The case worth thinking about is the degraded one. initializeKeepMobile() is deliberately wrapped in runCatching, so the app can be running with that having failed. Today a NIP-55 intent from another app would start the activity and fail later on an actual signing call. After this change the same state fails during class initialization, as an ExceptionInInitializerError, which surfaces to the calling app as an opaque crash rather than a handled error.

Narrow, and arguably a signer that cannot load its crypto library should not pretend otherwise, so I am not calling it a blocker. But it is a real change in failure mode for an activity that external apps invoke, and if you want to keep the old behaviour the cheapest fix is reading the cap where it is used rather than at class-init.

Everything else checks out: the import is correct, the comment states the ownership reason rather than just the mechanic, and the literal 20 is gone from the Kotlin side, which was the point.

[wksantiago]

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Actionable comments posted: 1

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Inline comments:
In `@keep.version`:
- Line 1: Update the keep.version pinned commit from
bd8ca8d3945572923e372efd43231caae2e195d9 to
750d8f5f44304b009ef1c45313999447020dbd9a.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: 190f4d64-006b-46f1-8bd5-155d7bd9be62

📥 Commits

Reviewing files that changed from the base of the PR and between fa70329 and 39118ed.

📒 Files selected for processing (2)

• app/src/main/kotlin/io/privkey/keep/nip55/Nip55Activity.kt
• keep.version

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

[wksantiago]

Thanks @kwsantiago — both addressed.

Blocker (pin): repinned keep.version to 750d8f5f44304b009ef1c45313999447020dbd9a, the squash-merge of #974 on keep's main (0ca29f0). Verified git merge-base --is-ancestor 750d8f5 origin/main → YES, so it's reachable via refs/heads/* and no longer only through the PR ref — the F-Droid srclib checkout path is fixed.

Observation (class-init failure mode): applied the use-site read (b18f1cf). MAX_BATCH_SIZE is now a computed get() rather than a stored val, and gate is by lazy, so nip55MaxBatchSize() is called on first request-handling use instead of at class-load. In the degraded state where initializeKeepMobile() failed, a NIP-55 intent now fails on the signing path as a handled error again, not an opaque ExceptionInInitializerError. Old failure timing preserved.

Verified locally with keep at the new pin: :app:compileDebugKotlin BUILD SUCCESSFUL, the generated binding still exposes nip55MaxBatchSize(), and no binding drift.

[kwsantiago]

Both confirmed independently on b18f1cf.

Pin. 750d8f5f is now an ancestor of keep's main and carried by refs/heads, so the srclib checkout resolves from a plain clone rather than depending on a pull ref surviving. Built keep-android against that commit directly and the binding generates.

Class-init. The pair is what makes this work, and the by lazy on gate is the half that mattered: a computed get() on its own would have left the FFI call in the instance initializer, so it would still have fired during Activity construction and only moved the failure from ExceptionInInitializerError to a construction-time throw. Deferring gate too pushes the first call into request handling, where every gate access already sits behind the runCatching guards on the intent and signing paths. That turns a class-poisoning error into a handled one, which is the behaviour the old const val had.

The computed getter does mean an FFI call per read, but there are only two readers — gate's lazy initialiser and a BuildConfig.DEBUG log on the drop path — so it is not worth caching back into a stored value and reintroducing the init-order question.

Verified: Pixel 9a, Android 17, 291 tests, 0 failures, 5 skipped, matching main. Local gate green (unit tests, lintDebug, RNG hygiene guard). CI green.

No blockers.