diff --git a/config/reliability-gates.jsonc b/config/reliability-gates.jsonc
index 12b937b187f..2a2980d2427 100644
--- a/config/reliability-gates.jsonc
+++ b/config/reliability-gates.jsonc
@@ -1,6 +1,6 @@
 {
   "schemaVersion": 1,
-  "updatedAt": "2026-08-20",
+  "updatedAt": "2026-08-23",
   "policy": {
     "maturityLevels": ["experimental", "soak", "blocking", "accepted-gap", "deprecated"],
     "blockingPromotion": {
@@ -2361,6 +2361,82 @@
       ],
       "demotionRule": "Demote if a reload revision settles more than once, a stale document or competing window can publish, a timer survives settlement, desktop failure stays indefinitely reloading, headless fallback returns after successful promotion, or either isolated Electron journey loses runtime or PTY identity."
     },
+    {
+      "id": "runtime.headless-renderer-process-containment",
+      "title": "Headless renderer process death stays isolated from runtime-owned PTYs",
+      "maturity": "experimental",
+      "protection": "partial",
+      "owner": "runtime-platform",
+      "layer": "electron-process-containment",
+      "surfaces": ["headless orca serve", "offscreen browser page", "daemon-backed PTYs"],
+      "platforms": ["macos", "linux", "windows"],
+      "providers": ["local", "daemon"],
+      "coveredPlatforms": ["macos"],
+      "coveredProviders": ["local", "daemon"],
+      "coverageNotes": "An isolated headless serve host creates two daemon-backed terminal sessions and one offscreen browser renderer. Exact WebContents and OS-process fencing prevents a fault from reaching an unrelated process. The oracle is host-local and does not claim paired-viewer continuity, renderer reload, systemd cgroup restart persistence, SSH or WSL coverage, or aggregate memory policy.",
+      "motivatingLinks": [
+        "https://linear.app/stably/issue/STA-5228",
+        "https://github.com/stablyai/orca/issues/16084",
+        "https://github.com/stablyai/orca/pull/16120"
+      ],
+      "invariant": "Killing one exact offscreen Chromium renderer cannot replace or terminate the headless main process, runtime, daemon, or unrelated daemon-backed PTYs. The host session inventory retains each original tab-to-PTY binding, and both original PTY processes continue accepting input.",
+      "oracle": "Start an isolated headless serve runtime with zero initial BrowserWindows, create two daemon-backed terminal fixtures, and record main, runtime, daemon, tab, PTY, fixture-process, WebContents, and renderer-process identities. Fence one marked offscreen page by WebContents, URL, and OS process, force that renderer to crash, and require its original process to die while main/runtime/daemon identities, both host tab-to-PTY bindings, and I/O through both original fixture processes remain unchanged.",
+      "commands": [
+        "pnpm exec electron-vite build --mode e2e",
+        "SKIP_BUILD=1 pnpm exec playwright test tests/e2e/headless-serve-renderer-kill-retention.spec.ts --config tests/playwright.config.ts --project electron-headless --workers=1"
+      ],
+      "testFiles": ["tests/e2e/headless-serve-renderer-kill-retention.spec.ts"],
+      "assertionRefs": [
+        {
+          "file": "tests/e2e/headless-serve-renderer-kill-retention.spec.ts",
+          "assertions": [
+            "the exact original renderer process dies after the fenced WebContents fault",
+            "main, runtime, and daemon identities remain unchanged and reachable",
+            "both original host tab-to-PTY bindings remain published",
+            "both original PTY processes accept post-fault input"
+          ]
+        }
+      ],
+      "evidenceRuns": [
+        {
+          "date": "2026-08-23",
+          "runner": "local",
+          "platform": "macos",
+          "command": "SKIP_BUILD=1 pnpm exec playwright test tests/e2e/headless-serve-renderer-kill-retention.spec.ts --config tests/playwright.config.ts --project electron-headless --workers=1",
+          "result": "passed",
+          "durationSeconds": 31,
+          "summary": "The exact offscreen renderer process died while the headless main process, runtime, daemon, both original host tab-to-PTY bindings, and both original PTY processes remained live; both PTYs accepted post-fault input."
+        }
+      ],
+      "runtimeBudget": {
+        "p95Seconds": 60,
+        "scope": "one isolated headless Electron host, one offscreen renderer fault, and two daemon-backed PTY fixtures"
+      },
+      "flakeHistory": {
+        "status": "unknown",
+        "evidence": "Fresh local macOS runs are green; CI and cross-platform soak history are not yet available."
+      },
+      "redGreenEvidence": {
+        "status": "partial",
+        "evidence": "The byte-identical oracle passes on reported v1.4.184 and current main, falsifying renderer-only death as the cause of runtime/session loss. The candidate adds characterization coverage only; reverting it removes the oracle without changing product behavior."
+      },
+      "performanceBudget": {
+        "required": false,
+        "evidence": "The change adds test and gate metadata only. Production startup, fault handling, session inventory, and PTY hot paths are unchanged."
+      },
+      "promotionCriteria": [
+        "Pass the changed-spec Ubuntu/Xvfb PR lane.",
+        "Collect at least 100 consecutive CI or soak passes or 14 days without an unexplained flake.",
+        "Add Windows containment evidence if Electron process behavior diverges."
+      ],
+      "knownGaps": [
+        "The fault is an exact WebContents renderer crash, not kernel OOM victim selection or systemd cgroup failure.",
+        "The host-local runtime client proves control-plane reachability but not a separate paired viewer, reconnect, or replay path.",
+        "The test does not require the crashed browser surface to recover; browser-page recovery is a separate lifecycle contract.",
+        "SSH, WSL, folder-workspace, multi-client, mixed-version, and whole-service restart journeys are uncollected; no production or wire behavior changes in this gate."
+      ],
+      "demotionRule": "Demote if the exact renderer fault changes main/runtime/daemon identity, removes either tab-to-PTY binding, replaces either fixture process, loses post-fault PTY I/O, or cannot identify the killed renderer unambiguously."
+    },
     {
       "id": "runtime.websocket-heartbeat-cadence",
       "title": "Runtime WebSockets enter an owned shared heartbeat cadence",
diff --git a/tests/e2e/headless-serve-renderer-kill-retention.spec.ts b/tests/e2e/headless-serve-renderer-kill-retention.spec.ts
index 5be02793184..819b0078a61 100644
--- a/tests/e2e/headless-serve-renderer-kill-retention.spec.ts
+++ b/tests/e2e/headless-serve-renderer-kill-retention.spec.ts
@@ -7,6 +7,7 @@ import { expect, test } from './helpers/orca-app'
 import {
   createHostCliTerminal,
   proveSameLivePty,
+  readHostTerminalInventory,
   writeRetentionFixture
 } from './helpers/host-created-terminal-retention-oracle'
 import { launchHeadlessPairedRuntimeHost } from './helpers/headless-paired-runtime-host'
@@ -114,6 +115,9 @@ test('STA-5228 renderer death keeps headless runtime and PTYs alive', async ({ t
     )
     await proveSameLivePty(call, terminalA, 'BEFORE_RENDERER_KILL_A')
     await proveSameLivePty(call, terminalB, 'BEFORE_RENDERER_KILL_B')
+    const beforeInventory = await readHostTerminalInventory(call, worktreeId)
+    expect(beforeInventory.ptyIdByTabId[terminalA.tabId]).toBe(terminalA.ptyId)
+    expect(beforeInventory.ptyIdByTabId[terminalB.tabId]).toBe(terminalB.ptyId)
 
     const pageId = `sta-5228-${Date.now()}`
     const markerUrl = `data:text/html,${encodeURIComponent(
@@ -212,13 +216,11 @@ test('STA-5228 renderer death keeps headless runtime and PTYs alive', async ({ t
     expect(await processIdentityIsAlive(daemonIdentity)).toBe(true)
     await proveSameLivePty(call, terminalA, 'AFTER_RENDERER_KILL_A')
     await proveSameLivePty(call, terminalB, 'AFTER_RENDERER_KILL_B')
+    const afterInventory = await readHostTerminalInventory(call, worktreeId)
+    expect(afterInventory.ptyIdByTabId[terminalA.tabId]).toBe(terminalA.ptyId)
+    expect(afterInventory.ptyIdByTabId[terminalB.tabId]).toBe(terminalB.ptyId)
 
     const afterRenderer = await readOffscreenRenderer(launchedHost.app, pageId, false)
-    expect(afterRenderer).toMatchObject({
-      crashed: true,
-      pid: 0,
-      webContentsId: renderer.webContentsId
-    })
     console.log('[STA-5228] renderer lifecycle snapshot', {
       afterRenderer,
       beforeRenderer: renderer,