diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 628d69b..06a9e9f 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -1,11 +1,11 @@
 name: Nightly
 
 on:
-  push:
+  pull_request:
     branches:
       - main
-  schedule:
-    - cron: "0 3 * * *"
+    types:
+      - closed
   workflow_dispatch:
 
 permissions:
@@ -17,6 +17,7 @@ concurrency:
 
 jobs:
   build-macos:
+    if: ${{ github.event_name != 'pull_request' || github.event.pull_request.merged == true }}
     name: Build nightly macOS (${{ matrix.arch }})
     runs-on: macos-15
     strategy:
@@ -61,6 +62,7 @@ jobs:
           path: dist/*
 
   publish-nightly:
+    if: ${{ github.event_name != 'pull_request' || github.event.pull_request.merged == true }}
     name: Publish Nightly Release
     runs-on: ubuntu-latest
     needs: [build-macos]
@@ -82,7 +84,9 @@ jobs:
         run: |
           set -euo pipefail
           NIGHTLY_VERSION="$(date -u +'%Y.%m.%d').${GITHUB_RUN_NUMBER}"
+          NIGHTLY_COMMIT="${{ github.event.pull_request.merge_commit_sha || github.sha }}"
           echo "NIGHTLY_VERSION=${NIGHTLY_VERSION}" >> "${GITHUB_ENV}"
+          echo "NIGHTLY_COMMIT=${NIGHTLY_COMMIT}" >> "${GITHUB_ENV}"
 
       - name: Publish nightly assets
         uses: softprops/action-gh-release@v2
@@ -93,7 +97,7 @@ jobs:
           make_latest: false
           generate_release_notes: false
           body: |
-            Nightly build for commit `${{ github.sha }}`.
+            Nightly build for commit `${{ env.NIGHTLY_COMMIT }}`.
             Version: `${{ env.NIGHTLY_VERSION }}`
           files: |
             dist/*.tar.gz
@@ -101,6 +105,7 @@ jobs:
           overwrite_files: true
 
   update-homebrew-tap-nightly:
+    if: ${{ github.event_name != 'pull_request' || github.event.pull_request.merged == true }}
     name: Update Homebrew Tap (nightly)
     runs-on: ubuntu-latest
     needs: [publish-nightly]
diff --git a/README.md b/README.md
index a9f2d9c..062473a 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,10 @@ Release automation included:
   - Builds `snapshot-report` for macOS `arm64` and `x86_64` on tag push (`v*`)
   - Uploads artifacts to GitHub Releases
   - Updates `oscarcv/tap` formula automatically
+- `.github/workflows/nightly.yml`
+  - Runs on PR merges into `main`
+  - Publishes/updates a moving `nightly` prerelease (`arm64` + `x86_64`)
+  - Updates `oscarcv/tap` nightly formula (`snapshot-report-nightly`)
 
 ## Examples
 
@@ -157,6 +161,18 @@ swift run snapshot-report \
   --output .artifacts/report
 ```
 
+### Verbose diagnostics
+
+Use `--verbose` to print detailed processing diagnostics (inputs, phase progress, odiff usage, and timings):
+
+```bash
+swift run snapshot-report \
+  --input-dir .artifacts/snapshot-runs \
+  --output .artifacts/report \
+  --format json,junit,html \
+  --verbose
+```
+
 ### odiff pixel diff
 
 [odiff](https://github.com/dmtrKovalenko/odiff) is a SIMD-accelerated image diff tool that produces highlighted difference images. Install it first:
diff --git a/Sources/snapshot-report/CLI/main.swift b/Sources/snapshot-report/CLI/main.swift
index ea3f92a..ac16aaf 100644
--- a/Sources/snapshot-report/CLI/main.swift
+++ b/Sources/snapshot-report/CLI/main.swift
@@ -5,7 +5,6 @@ import SnapshotReportCLI
 
 struct CLI {
     static func run() throws {
-        CLIUI.header("snapshot-report")
         let arguments = Array(CommandLine.arguments.dropFirst())
 
         if arguments.first == "inspect" {
@@ -19,10 +18,14 @@ struct CLI {
         }
 
         let options = try parse(arguments: arguments)
+        CLIUI.setVerbose(options.verbose)
+        CLIUI.header("snapshot-report")
         try FileManager.default.createDirectory(at: options.outputDirectory, withIntermediateDirectories: true)
 
+        let startedAt = Date()
         CLIUI.step("Resolving input files")
         let resolvedInputs = try resolveInputs(options: options)
+        CLIUI.debug("Resolved \(resolvedInputs.count) JSON inputs and \(options.xcresultInputs.count) xcresult inputs")
 
         CLIUI.step("Loading JSON reports (\(resolvedInputs.count))")
         let reports = try _loadJSONReports(inputs: resolvedInputs, jobs: options.jobs) { completed, total, input in
@@ -36,13 +39,16 @@ struct CLI {
 
         CLIUI.step("Merging report data")
         let mergedReport = SnapshotReportAggregator.merge(reports: reports + xcresultReports, name: options.reportName)
+        CLIUI.debug("Merged report: \(mergedReport.summary.total) tests (\(mergedReport.summary.passed) passed, \(mergedReport.summary.failed) failed, \(mergedReport.summary.skipped) skipped)")
 
         let effectiveOdiffPath = options.odiffPath ?? _resolveOnPATH("odiff")
         let finalReport: SnapshotReport
         if let odiffPath = effectiveOdiffPath {
             CLIUI.step("Generating odiff attachments")
+            CLIUI.debug("Using odiff binary: \(odiffPath)")
             finalReport = OdiffProcessor(odiffBinaryPath: odiffPath).process(report: mergedReport)
         } else {
+            CLIUI.debug("odiff not found; skipping diff enrichment")
             finalReport = mergedReport
         }
 
@@ -57,6 +63,8 @@ struct CLI {
             CLIUI.progress("Output \(completed)/\(total): \(format.rawValue)")
         }
 
+        let elapsed = Date().timeIntervalSince(startedAt)
+        CLIUI.debug(String(format: "Total processing time: %.3fs", elapsed))
         CLIUI.success("Generated report \(options.formats.map(\.rawValue).joined(separator: ", ")) at \(options.outputDirectory.path)")
     }
 
@@ -70,6 +78,7 @@ struct CLI {
         var reportName: String?
         var odiffPath: String?
         var jobs = max(1, ProcessInfo.processInfo.activeProcessorCount)
+        var verbose = false
 
         var index = 0
         while index < arguments.count {
@@ -122,6 +131,8 @@ struct CLI {
                     throw SnapshotReportError.invalidInput("--jobs must be a positive integer")
                 }
                 jobs = parsed
+            case "--verbose", "-v":
+                verbose = true
             default:
                 throw SnapshotReportError.invalidInput("Unknown argument: \(argument)")
             }
@@ -142,7 +153,8 @@ struct CLI {
             htmlTemplate: htmlTemplate,
             reportName: reportName,
             odiffPath: odiffPath,
-            jobs: jobs
+            jobs: jobs,
+            verbose: verbose
         )
     }
 
@@ -191,6 +203,7 @@ struct CLI {
                   --name <string>         Override merged report name
                   --odiff <path>          Path to odiff binary (default: auto-detect on PATH)
                   --jobs <n>              Max parallel xcresult reads (default: CPU count)
+              -v, --verbose               Enable diagnostic output
                   --help                  Show help
             """
         )
@@ -206,6 +219,7 @@ struct CLI {
         let reportName: String?
         let odiffPath: String?
         let jobs: Int
+        let verbose: Bool
     }
 }
 
@@ -421,17 +435,34 @@ private final class ReportWriteState: @unchecked Sendable {
 private enum CLIUI {
     private static let lock = NSLock()
     private static let prefix = "[snapshot-report]"
+    private static let state = VerboseState()
+
+    static func setVerbose(_ value: Bool) {
+        state.set(value)
+    }
 
     static func header(_ title: String) {
-        log("\(prefix) \(title)")
+        if verboseEnabled() {
+            log("\(prefix) \(title)")
+        }
     }
 
     static func step(_ message: String) {
-        log("\(prefix) step: \(message)")
+        if verboseEnabled() {
+            log("\(prefix) step: \(message)")
+        }
     }
 
     static func progress(_ message: String) {
-        log("\(prefix) progress: \(message)")
+        if verboseEnabled() {
+            log("\(prefix) progress: \(message)")
+        }
+    }
+
+    static func debug(_ message: String) {
+        if verboseEnabled() {
+            log("\(prefix) debug: \(message)")
+        }
     }
 
     static func success(_ message: String) {
@@ -443,6 +474,27 @@ private enum CLIUI {
         print(message)
         lock.unlock()
     }
+
+    private static func verboseEnabled() -> Bool {
+        state.get()
+    }
+}
+
+private final class VerboseState: @unchecked Sendable {
+    private let lock = NSLock()
+    private var value = false
+
+    func set(_ newValue: Bool) {
+        lock.lock()
+        value = newValue
+        lock.unlock()
+    }
+
+    func get() -> Bool {
+        lock.lock()
+        defer { lock.unlock() }
+        return value
+    }
 }
 
 private func _resolveOnPATH(_ name: String) -> String? {