test: add E2E steps for history delta and tests-changed

.github/workflows/e2e.yml

@@ -86,6 +86,32 @@ jobs:
           test-job-name: my-custom-job
           slowest-tests: '0'
 
+      # ── History features (Epic 7): delta, tests changed, trends ──
+      # Both steps use the same report-path (same cache key hash).
+      # Step 1 seeds the cache with baseline data; the copy swaps in
+      # different results; step 2 restores history and shows diffs.
+      # Over successive main runs, cross-run history accumulates and
+      # enables flaky detection, perf regression, and trend indicators.
+      - name: 'History: prepare baseline'
+        run: cp fixtures/e2e-history-base.xml fixtures/e2e-history.xml
+
+      - name: 'History: seed baseline'
+        uses: ./
+        with:
+          api-key: unused
+          send-results: false
+          report-path: fixtures/e2e-history.xml
+
+      - name: 'History: swap to changed fixture'
+        run: cp fixtures/e2e-history-changed.xml fixtures/e2e-history.xml
+
+      - name: 'History: delta + tests changed'
+        uses: ./
+        with:
+          api-key: unused
+          send-results: false
+          report-path: fixtures/e2e-history.xml
+
       # ── Edge cases: must warn but NOT fail ──
       - name: 'Edge: malformed XML (should warn, exit 0)'
         uses: ./

fixtures/e2e-history-base.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<testsuite name="e2e-history" tests="5" failures="1" errors="0" skipped="0" time="3.100">
+  <testcase name="should create user" classname="api.users" time="0.800"/>
+  <testcase name="should list users" classname="api.users" time="0.500"/>
+  <testcase name="should delete user" classname="api.users" time="0.300"/>
+  <testcase name="should update profile" classname="api.profile" time="1.000"/>
+  <testcase name="should validate email" classname="api.profile" time="0.500">
+    <failure message="Invalid email not rejected">AssertionError: expected 400 but got 200</failure>
+  </testcase>
+</testsuite>

fixtures/e2e-history-changed.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<testsuite name="e2e-history" tests="5" failures="1" errors="0" skipped="0" time="5.400">
+  <testcase name="should create user" classname="api.users" time="0.900"/>
+  <testcase name="should list users" classname="api.users" time="0.600"/>
+  <testcase name="should update profile" classname="api.profile" time="4.200">
+    <failure message="Timeout waiting for response">TimeoutError: 4200ms exceeded</failure>
+  </testcase>
+  <testcase name="should validate email" classname="api.profile" time="0.400"/>
+  <testcase name="should upload avatar" classname="api.profile" time="0.300"/>
+</testsuite>