diff --git a/.github/actions/swift-packages/action.yml b/.github/actions/swift-packages/action.yml
new file mode 100644
index 000000000..a4c91b195
--- /dev/null
+++ b/.github/actions/swift-packages/action.yml
@@ -0,0 +1,53 @@
+name: Swift packages
+description: >
+  Resolves the Swift packages into $SOURCE_PACKAGES and caches them. Pass
+  -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" -disableAutomaticPackageResolution
+  -skipPackageUpdates to every later xcodebuild call, or it resolves and clones everything again.
+
+# SwiftPM keeps a full bare clone of every package and looks each one up on every resolve, so
+# the clones have to be cached too. bitkit-core's history alone is over 13 GB, past the
+# repository cache limit, so on a miss the clones are cut down to the pinned commits first.
+runs:
+  using: composite
+  steps:
+    - name: Locate Swift packages
+      id: locate
+      shell: bash
+      run: |
+        echo "SOURCE_PACKAGES=$GITHUB_WORKSPACE/SourcePackages" >> "$GITHUB_ENV"
+        echo "xcode=$(xcodebuild -version | head -1 | cut -d' ' -f2)" >> "$GITHUB_OUTPUT"
+
+    - name: Restore Swift packages
+      id: cache
+      uses: actions/cache/restore@v6
+      with:
+        path: ${{ github.workspace }}/SourcePackages
+        key: ${{ runner.os }}-xcode-${{ steps.locate.outputs.xcode }}-source-packages-v2-${{ hashFiles('Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm/Package.resolved') }}
+
+    - name: Resolve Swift packages
+      shell: bash
+      run: |
+        echo "⏱️  Starting dependency resolution at $(date)"
+        set -o pipefail && xcodebuild -resolvePackageDependencies \
+          -scheme Bitkit \
+          -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+          -disablePackageRepositoryCache \
+          -onlyUsePackageVersionsFromResolvedFile \
+          -skipPackageUpdates \
+          | xcbeautify
+        echo "✅ Dependencies resolved at $(date)"
+
+    - name: Shrink package clones
+      if: steps.cache.outputs.cache-hit != 'true'
+      shell: bash
+      run: |
+        "$GITHUB_WORKSPACE/scripts/shallow-source-packages.sh" "$SOURCE_PACKAGES"
+        du -sh "$SOURCE_PACKAGES"
+
+    # Saved right after resolving so a failing job still warms the cache.
+    - name: Save Swift packages
+      if: steps.cache.outputs.cache-hit != 'true'
+      uses: actions/cache/save@v6
+      with:
+        path: ${{ github.workspace }}/SourcePackages
+        key: ${{ steps.cache.outputs.cache-primary-key }}
diff --git a/.github/workflows/e2e-staging.yml b/.github/workflows/e2e-staging.yml
index dddbbfa21..af24b7b29 100644
--- a/.github/workflows/e2e-staging.yml
+++ b/.github/workflows/e2e-staging.yml
@@ -52,20 +52,8 @@ jobs:
         run: |
           brew install xcbeautify
 
-      - name: Cache Swift Package Manager
-        uses: actions/cache@v6
-        with:
-          path: |
-            ~/Library/Caches/org.swift.swiftpm
-            ~/Library/org.swift.swiftpm
-            Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm
-          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
-
-      - name: Install dependencies
-        run: |
-          echo "⏱️  Starting dependency resolution at $(date)"
-          xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile | xcbeautify
-          echo "✅ Dependencies resolved at $(date)"
+      - name: Swift packages
+        uses: ./.github/actions/swift-packages
 
       - name: Pre-start simulator
         run: |
@@ -96,6 +84,10 @@ jobs:
             -configuration Debug \
             -destination "platform=iOS Simulator,name=${{ env.SIMULATOR_NAME }},OS=${{ env.IOS_VERSION }}" \
             -derivedDataPath DerivedData \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
             SWIFT_ACTIVE_COMPILATION_CONDITIONS='DEBUG E2E_BUILD' \
             -allowProvisioningUpdates \
             build
diff --git a/.github/workflows/e2e-tests.yml b/.github/workflows/e2e-tests.yml
index 3c59e1d9d..b0f739e28 100644
--- a/.github/workflows/e2e-tests.yml
+++ b/.github/workflows/e2e-tests.yml
@@ -77,20 +77,8 @@ jobs:
         run: |
           brew install xcbeautify
 
-      - name: Cache Swift Package Manager
-        uses: actions/cache@v6
-        with:
-          path: |
-            ~/Library/Caches/org.swift.swiftpm
-            ~/Library/org.swift.swiftpm
-            Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm
-          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
-
-      - name: Install dependencies
-        run: |
-          echo "⏱️  Starting dependency resolution at $(date)"
-          xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile | xcbeautify
-          echo "✅ Dependencies resolved at $(date)"
+      - name: Swift packages
+        uses: ./.github/actions/swift-packages
 
       - name: Pre-start simulator
         run: |
@@ -122,6 +110,10 @@ jobs:
             -configuration Debug \
             -destination "platform=iOS Simulator,name=$SIMULATOR_NAME,OS=$OS_VERSION" \
             -derivedDataPath DerivedData \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
             SWIFT_ACTIVE_COMPILATION_CONDITIONS='DEBUG E2E_BUILD' \
             TREZOR_BRIDGE=true \
             TREZOR_BRIDGE_URL=http://127.0.0.1:21325 \
diff --git a/.github/workflows/e2e_migration.yml b/.github/workflows/e2e_migration.yml
index 94d9e9e40..b115803e5 100644
--- a/.github/workflows/e2e_migration.yml
+++ b/.github/workflows/e2e_migration.yml
@@ -63,20 +63,8 @@ jobs:
         run: |
           brew install xcbeautify
 
-      - name: Cache Swift Package Manager
-        uses: actions/cache@v6
-        with:
-          path: |
-            ~/Library/Caches/org.swift.swiftpm
-            ~/Library/org.swift.swiftpm
-            Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm
-          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
-
-      - name: Install dependencies
-        run: |
-          echo "⏱️  Starting dependency resolution at $(date)"
-          xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile | xcbeautify
-          echo "✅ Dependencies resolved at $(date)"
+      - name: Swift packages
+        uses: ./.github/actions/swift-packages
 
       - name: Pre-start simulator
         run: |
@@ -108,6 +96,10 @@ jobs:
             -configuration Debug \
             -destination "platform=iOS Simulator,name=${{ env.SIMULATOR_NAME }},OS=${{ env.IOS_VERSION }}" \
             -derivedDataPath DerivedData \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
             SWIFT_ACTIVE_COMPILATION_CONDITIONS='$(inherited) E2E_BUILD' \
             -allowProvisioningUpdates \
             build
diff --git a/.github/workflows/integration-tests.yml b/.github/workflows/integration-tests.yml
index 6867a0637..927863b3a 100644
--- a/.github/workflows/integration-tests.yml
+++ b/.github/workflows/integration-tests.yml
@@ -22,6 +22,9 @@ jobs:
     name: Run Integration Tests
     runs-on: macos-15
     timeout-minutes: 60
+    env:
+      DERIVED_DATA: ${{ github.workspace }}/DerivedData
+      RESULT_BUNDLE: ${{ github.workspace }}/IntegrationTests.xcresult
 
     steps:
       - name: Checkout repository
@@ -32,81 +35,85 @@ jobs:
         with:
           xcode-version: '16.4'
 
+      # A fresh simulator takes over 10 minutes to boot on the runner. Booting it now lets that
+      # overlap with resolving and building instead of stalling the test step.
+      - name: Boot simulator
+        run: |
+          udid=$(xcrun simctl list devices available -j | python3 -c '
+          import json, sys
+          runtimes = json.load(sys.stdin)["devices"]
+          version = lambda runtime: [int(part) for part in runtime.rsplit(".", 1)[-1].split("-")[1:]]
+          ios = sorted((r for r in runtimes if ".iOS-" in r and any(d["name"] == "iPhone 16" for d in runtimes[r])), key=version)
+          print(next(d["udid"] for d in runtimes[ios[-1]] if d["name"] == "iPhone 16"))
+          ')
+          echo "SIMULATOR_UDID=$udid" >> "$GITHUB_ENV"
+          echo "DESTINATION=platform=iOS Simulator,id=$udid" >> "$GITHUB_ENV"
+          xcrun simctl boot "$udid"
+
       - name: Install xcbeautify
         run: |
           brew install xcbeautify
 
-      - name: Cache Swift Package Manager
-        uses: actions/cache@v6
-        with:
-          path: |
-            ~/Library/Caches/org.swift.swiftpm
-            ~/Library/org.swift.swiftpm
-            Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm
-          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
-
-      - name: Install dependencies
-        run: |
-          echo "⏱️  Starting dependency resolution at $(date)"
-          xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile | xcbeautify
-          echo "✅ Dependencies resolved at $(date)"
+      - name: Swift packages
+        uses: ./.github/actions/swift-packages
 
-      - name: Clean build
+      - name: Build for testing
         run: |
-          echo "⏱️  Cleaning build at $(date)"
-          xcodebuild clean -scheme Bitkit | xcbeautify
-          echo "✅ Build cleaned at $(date)"
+          echo "⏱️  Starting build at $(date)"
+          set -o pipefail && xcodebuild build-for-testing \
+            -scheme Bitkit \
+            -destination "$DESTINATION" \
+            -derivedDataPath "$DERIVED_DATA" \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
+            -enableCodeCoverage NO \
+            | xcbeautify
+          echo "✅ Build finished at $(date)"
 
       - name: Run integration tests
+        timeout-minutes: 25
         run: |
+          xcrun simctl bootstatus "$SIMULATOR_UDID" -b
           echo "⏱️  Starting integration tests at $(date)"
 
-          run_tests() {
-            # RNMigrationCleanupTests deletes the real ~/Documents/mmkv and ~/Documents/ldk, so it
-            # skips itself unless this is set. This lane runs on a simulator it erases between
-            # attempts; the unit lane does not, and must not run it.
-            #
-            # The TEST_RUNNER_ prefix is required: xcodebuild does not pass the invoking shell's
-            # environment to the simulator-hosted runner, only variables named TEST_RUNNER_<VAR>,
-            # which it forwards with the prefix stripped. Without it the guard never sees the
-            # variable, every test in the suite skips, and the lane still reports green.
-            set -o pipefail && TEST_RUNNER_BITKIT_DESTRUCTIVE_TESTS=1 xcodebuild test \
-              -scheme Bitkit \
-              -destination 'platform=iOS Simulator,name=iPhone 16,OS=latest' \
-              -enableCodeCoverage NO \
-              -parallel-testing-enabled NO \
-              -only-testing:BitkitTests/UtxoSelectionTests \
-              -only-testing:BitkitTests/BlocktankTests \
-              -only-testing:BitkitTests/PaymentFlowTests \
-              -only-testing:BitkitTests/BlocktankRefundAddressLiveIntegrationTests \
-              -only-testing:BitkitTests/AddressTypeIntegrationTests \
-              -only-testing:BitkitTests/RNMigrationCleanupTests \
-              | xcbeautify --report junit
-          }
-
-          # Try up to 3 times with simulator reset between failures
-          for attempt in 1 2 3; do
-            echo "🔄 Test attempt $attempt of 3"
-            if run_tests; then
-              echo "✅ Integration tests completed at $(date)"
-              exit 0
-            fi
-
-            if [ $attempt -lt 3 ]; then
-              echo "⚠️  Test attempt $attempt failed, resetting simulator..."
-              xcrun simctl shutdown all || true
-              xcrun simctl erase "iPhone 16" || true
-              xcrun simctl boot "iPhone 16"
-              sleep 5
-            fi
-          done
-
-          echo "❌ All test attempts failed"
-          exit 1
+          # RNMigrationCleanupTests deletes the real ~/Documents/mmkv and ~/Documents/ldk, so it
+          # skips itself unless this is set. This lane runs on a throwaway CI simulator; the unit
+          # lane does not, and must not run it.
+          #
+          # The TEST_RUNNER_ prefix is required: xcodebuild does not pass the invoking shell's
+          # environment to the simulator-hosted runner, only variables named TEST_RUNNER_<VAR>,
+          # which it forwards with the prefix stripped. Without it the guard never sees the
+          # variable, every test in the suite skips, and the lane still reports green.
+          #
+          # The live regtest suites are flaky on CI runners, so a failed test is retried once on
+          # its own instead of rebuilding and rerunning the whole suite.
+          set -o pipefail && TEST_RUNNER_BITKIT_DESTRUCTIVE_TESTS=1 xcodebuild test-without-building \
+            -scheme Bitkit \
+            -destination "$DESTINATION" \
+            -derivedDataPath "$DERIVED_DATA" \
+            -resultBundlePath "$RESULT_BUNDLE" \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
+            -enableCodeCoverage NO \
+            -parallel-testing-enabled NO \
+            -retry-tests-on-failure \
+            -test-iterations 2 \
+            -only-testing:BitkitTests/UtxoSelectionTests \
+            -only-testing:BitkitTests/BlocktankTests \
+            -only-testing:BitkitTests/PaymentFlowTests \
+            -only-testing:BitkitTests/BlocktankRefundAddressLiveIntegrationTests \
+            -only-testing:BitkitTests/AddressTypeIntegrationTests \
+            -only-testing:BitkitTests/RNMigrationCleanupTests \
+            | xcbeautify --report junit
+          echo "✅ Integration tests completed at $(date)"
 
       - name: Upload test results
         uses: actions/upload-artifact@v7
         if: success() || failure()
         with:
           name: integration-test-results
-          path: ~/Library/Developer/Xcode/DerivedData/**/Logs/Test/*.xcresult
+          path: ${{ env.RESULT_BUNDLE }}
diff --git a/.github/workflows/unit-tests.yml b/.github/workflows/unit-tests.yml
index e3b85ff8a..0a83d0d07 100644
--- a/.github/workflows/unit-tests.yml
+++ b/.github/workflows/unit-tests.yml
@@ -35,20 +35,8 @@ jobs:
         run: |
           brew install xcbeautify
 
-      - name: Cache Swift Package Manager
-        uses: actions/cache@v6
-        with:
-          path: |
-            ~/Library/Caches/org.swift.swiftpm
-            ~/Library/org.swift.swiftpm
-            Bitkit.xcodeproj/project.xcworkspace/xcshareddata/swiftpm
-          key: ${{ runner.os }}-spm-${{ hashFiles('**/Package.resolved') }}
-
-      - name: Install dependencies
-        run: |
-          echo "⏱️  Starting dependency resolution at $(date)"
-          xcodebuild -resolvePackageDependencies -onlyUsePackageVersionsFromResolvedFile | xcbeautify
-          echo "✅ Dependencies resolved at $(date)"
+      - name: Swift packages
+        uses: ./.github/actions/swift-packages
 
       - name: Pre-start simulator
         run: |
@@ -56,18 +44,16 @@ jobs:
           xcrun simctl boot "iPhone 16" || true
           echo "✅ Simulator started at $(date)"
 
-      - name: Clean build
-        run: |
-          echo "⏱️  Cleaning build at $(date)"
-          xcodebuild clean -scheme Bitkit | xcbeautify
-          echo "✅ Build cleaned at $(date)"
-
       - name: Run unit tests
         run: |
           echo "⏱️  Starting unit tests at $(date)"
           set -o pipefail && xcodebuild test \
             -scheme Bitkit \
             -destination 'platform=iOS Simulator,name=iPhone 16,OS=latest' \
+            -clonedSourcePackagesDirPath "$SOURCE_PACKAGES" \
+            -disablePackageRepositoryCache \
+            -disableAutomaticPackageResolution \
+            -skipPackageUpdates \
             -enableCodeCoverage NO \
             -parallel-testing-enabled NO \
             -skip-testing:BitkitTests/UtxoSelectionTests \
diff --git a/BitkitTests/UtxoSelectionTests.swift b/BitkitTests/UtxoSelectionTests.swift
index f05058b6f..4e5e0e7d3 100644
--- a/BitkitTests/UtxoSelectionTests.swift
+++ b/BitkitTests/UtxoSelectionTests.swift
@@ -8,6 +8,42 @@ final class UtxoSelectionTests: XCTestCase {
     let blocktank = CoreService.shared.blocktank
     let lightning = LightningService.shared
 
+    private static let pollIntervalNanoseconds: UInt64 = 2_000_000_000
+    private static let pollTimeout: TimeInterval = 120
+
+    /// Thrown rather than recorded, so a test whose funding never confirmed stops before it spends.
+    private struct PollTimeout: Error, CustomStringConvertible {
+        let description: String
+    }
+
+    /// Syncs and lists spendable outputs until `isReady` holds. Regtest confirmations reach the
+    /// node at varying speed on CI, and a sync can fail with `NodeError.WalletOperationTimeout`,
+    /// so a fixed sleep then a single sync sees partial state.
+    private func waitForSpendableOutputs(
+        _ description: String,
+        until isReady: ([SpendableUtxo]) -> Bool
+    ) async throws -> [SpendableUtxo] {
+        let deadline = Date().addingTimeInterval(Self.pollTimeout)
+        var outputs: [SpendableUtxo] = []
+
+        repeat {
+            do {
+                try await lightning.sync()
+                outputs = try await lightning.listSpendableOutputs()
+                if isReady(outputs) {
+                    return outputs
+                }
+                Logger.test("Waiting for \(description), have \(outputs.count) spendable outputs", context: "UtxoSelectionTests")
+            } catch {
+                Logger.test("Spendable output poll failed, retrying: \(error)", context: "UtxoSelectionTests")
+            }
+
+            try await Task.sleep(nanoseconds: Self.pollIntervalNanoseconds)
+        } while Date() < deadline
+
+        throw PollTimeout(description: "Timed out after \(Int(Self.pollTimeout))s waiting for \(description), last saw \(outputs.count) outputs")
+    }
+
     override func setUp() async throws {
         try await super.setUp()
         // `StartupHandler.createNewWallet` resets `selectedAddressType` and `addressTypesToMonitor` for a
@@ -95,15 +131,9 @@ final class UtxoSelectionTests: XCTestCase {
         try await blocktank.regtestMineBlocks(6)
         Logger.test("Blocks mined successfully", context: "UtxoSelectionTests")
 
-        // Sleep 15 seconds to ensure all blocks are processed
-        Logger.test("Waiting 15 seconds for blocks to be processed", context: "UtxoSelectionTests")
-        try await Task.sleep(nanoseconds: 15_000_000_000)
-        Logger.test("Wait completed", context: "UtxoSelectionTests")
-
-        // Sync the wallet to see the new balance
-        Logger.test("Syncing wallet to update balances", context: "UtxoSelectionTests")
-        try await lightning.sync()
-        Logger.test("Wallet sync complete", context: "UtxoSelectionTests")
+        let outputs = try await waitForSpendableOutputs("\(depositAmounts.count) confirmed deposits") {
+            $0.count >= depositAmounts.count
+        }
 
         // Verify updated balances after funding
         let updatedBalances = await MainActor.run { lightning.balances }
@@ -117,9 +147,7 @@ final class UtxoSelectionTests: XCTestCase {
         XCTAssertEqual(finalTotal, totalExpectedAmount, "Final balance should equal the sum of all deposits")
         XCTAssertGreaterThan(finalTotal, 0, "Final balance should be greater than 0")
 
-        // List utxos and make sure we have the right amount
-        Logger.test("Listing UTXOs to verify amounts", context: "UtxoSelectionTests")
-        let outputs = try await lightning.listSpendableOutputs()
+        // Make sure we have the right UTXOs
         Logger.test("Found \(outputs.count) spendable outputs", context: "UtxoSelectionTests")
         XCTAssertEqual(outputs.count, depositAmounts.count, "Number of UTXOs should match number of deposits")
 
@@ -184,19 +212,10 @@ final class UtxoSelectionTests: XCTestCase {
         try await blocktank.regtestMineBlocks(1)
         Logger.test("Block mined successfully", context: "UtxoSelectionTests")
 
-        // Wait for the block to be processed
-        Logger.test("Waiting 10 seconds for block to be processed", context: "UtxoSelectionTests")
-        try await Task.sleep(nanoseconds: 10_000_000_000)
-        Logger.test("Wait completed", context: "UtxoSelectionTests")
-
-        // Sync the wallet to update UTXOs
-        Logger.test("Syncing wallet to update UTXO set", context: "UtxoSelectionTests")
-        try await lightning.sync()
-        Logger.test("Wallet sync complete", context: "UtxoSelectionTests")
-
-        // List UTXOs again and verify the spent ones are missing
-        Logger.test("Listing UTXOs after spending to verify the spent ones are missing", context: "UtxoSelectionTests")
-        let remainingOutputs = try await lightning.listSpendableOutputs()
+        // Verify the spent ones are missing
+        let remainingOutputs = try await waitForSpendableOutputs("the selected UTXOs to be spent") { outputs in
+            !outputs.contains { output in selectedUtxoIds.contains("\(output.outpoint.txid):\(output.outpoint.vout)") }
+        }
         Logger.test("Found \(remainingOutputs.count) remaining spendable outputs", context: "UtxoSelectionTests")
 
         // Verify the specific UTXOs we spent are no longer in the list
@@ -271,19 +290,9 @@ final class UtxoSelectionTests: XCTestCase {
         try await blocktank.regtestMineBlocks(6)
         Logger.test("Blocks mined successfully", context: "UtxoSelectionTests")
 
-        // Wait for blocks to be processed
-        Logger.test("Waiting 15 seconds for blocks to be processed", context: "UtxoSelectionTests")
-        try await Task.sleep(nanoseconds: 15_000_000_000)
-        Logger.test("Wait completed", context: "UtxoSelectionTests")
-
-        // Sync the wallet to see the new balance
-        Logger.test("Syncing wallet to update balances", context: "UtxoSelectionTests")
-        try await lightning.sync()
-        Logger.test("Wallet sync complete", context: "UtxoSelectionTests")
-
-        // Get all available UTXOs
-        Logger.test("Listing all available UTXOs", context: "UtxoSelectionTests")
-        let allUtxos = try await lightning.listSpendableOutputs()
+        let allUtxos = try await waitForSpendableOutputs("\(depositAmounts.count) confirmed deposits") {
+            $0.count >= depositAmounts.count
+        }
         Logger.test("Found \(allUtxos.count) spendable outputs", context: "UtxoSelectionTests")
         XCTAssertEqual(allUtxos.count, depositAmounts.count, "Number of UTXOs should match number of deposits")
 
diff --git a/scripts/shallow-source-packages.sh b/scripts/shallow-source-packages.sh
new file mode 100755
index 000000000..596ca86e8
--- /dev/null
+++ b/scripts/shallow-source-packages.sh
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Shrinks SwiftPM's package clones to the pinned commits so CI can cache them.
+#
+# SwiftPM keeps a full bare clone of every package under <SourcePackages>/repositories, and
+# looks each one up again on every resolve (bitkit-core's history alone is over 13 GB, past
+# the repository cache limit). This keeps, for each clone, only the commit its checkout is
+# on plus the tags pointing at it, and drops the checkouts' own refs to commits that are gone.
+#
+# Usage: scripts/shallow-source-packages.sh <SourcePackages dir>
+set -euo pipefail
+
+source_packages="${1:?usage: $0 <SourcePackages dir>}"
+
+for checkout in "$source_packages"/checkouts/*/; do
+    checkout="${checkout%/}"
+    alternates="$checkout/.git/objects/info/alternates"
+    [ -f "$alternates" ] || continue
+    repository="$(dirname "$(cat "$alternates")")"
+    revision="$(git -C "$checkout" rev-parse HEAD)"
+
+    shallow="$repository.shallow"
+    rm -rf "$shallow"
+    git init -q --bare "$shallow"
+    cp "$repository/config" "$shallow/config"
+    git -C "$repository" config uploadpack.allowAnySHA1InWant true
+
+    refspecs=("$revision:refs/heads/pinned")
+    while read -r tag; do
+        [ -n "$tag" ] && refspecs+=("refs/tags/$tag:refs/tags/$tag")
+    done < <(git -C "$repository" tag --points-at "$revision")
+    git -C "$shallow" fetch -q --depth 1 --no-tags "file://$repository" "${refspecs[@]}"
+
+    rm -rf "$repository"
+    mv "$shallow" "$repository"
+
+    cp "$repository/shallow" "$checkout/.git/shallow"
+    git -C "$checkout" update-ref --no-deref HEAD "$revision"
+    git -C "$checkout" for-each-ref --format='%(refname)' | while read -r ref; do
+        git -C "$checkout" update-ref -d --no-deref "$ref"
+    done
+    rm -rf "$checkout/.git/logs"
+
+    echo "$(basename "$checkout"): $(du -sh "$repository" | cut -f1) at ${revision:0:7}"
+done