chore(booter): complete P2P/POSIX roadmap — ctx 1.48, VFS, shell, docs

- Bump bareOsCtxApiVersion to 1.48.0; sync CHANGELOG, compatibility matrix,
  syscalls.example.json, ctx d.ts, generated ctx-client helper
- POSIX: getconf _SC_NPROCESSORS_ONLN; shell set -o pipefail + BARE_OS_PIPESTATUS;
  posix_utilities schema v2 + JSON Schema; generated dashboard refresh
- Host/subprocess: bare-subprocess then Node child_process spawn; optional
  backend on ctx.bareOsTrySpawnHostSubprocess; bin-worker WASM wall budget
- VFS: BARE_OS_VFS_SYSTEM_IMAGE_WRITE for system image writes + warm-cache
  eviction path; guest /.bare/account EACCES test; environ TOKEN redaction test
- Docs: corestore snapshot non-goal in package-bare-os-booter; PEAR-RUN links
  → docs/PEAR-RUN.md; POSIX pretest matrix in scripts/README + dev guide;
  environment appendix (PIPESTATUS, WASM_MS, system image write)
- Seeder: keep kernel/ mirror in sync after bundle + coreutils builds

Verified: npm test -w bare-os-booter, npm run pretest

kernel/lib/init/init-main.js

@@ -2576,6 +2576,49 @@ async function verifyKernelExtSignerPinsForScript(
   return !strictPol
 }
 
+/**
+ * Append one NDJSON line to `/run/bare-os/kernel-ext-audit.ndjson` (strict boot diagnostics).
+ * @param {Record<string, unknown>} ctx
+ * @param {Record<string, unknown>} row
+ */
+async function appendKernelExtAuditNdjson(ctx, row) {
+  if (
+    !ctx.vfs ||
+    typeof ctx.vfs.readFile !== 'function' ||
+    typeof ctx.vfs.writeFile !== 'function' ||
+    !ctx.b4a
+  ) {
+    return
+  }
+  const line =
+    JSON.stringify({
+      schema: 1,
+      type: 'kernelExtAudit',
+      atMs: Date.now(),
+      sessionId: String((ctx.env && ctx.env.BARE_OS_SESSION_ID) || ''),
+      ...row
+    }) + '\n'
+  try {
+    let prev = ''
+    try {
+      prev = ctx.b4a.toString(
+        await ctx.vfs.readFile('/run/bare-os/kernel-ext-audit.ndjson')
+      )
+    } catch {
+      /* absent */
+    }
+    const maxBytes = 96 * 1024
+    let next = prev + line
+    if (next.length > maxBytes) next = next.slice(-maxBytes)
+    await ctx.vfs.writeFile(
+      '/run/bare-os/kernel-ext-audit.ndjson',
+      ctx.b4a.from(next)
+    )
+  } catch {
+    /* ignore */
+  }
+}
+
 /**
  * Optional `/etc/bare-os/kernel.ext.d/*.json` with `{ "scripts": ["/lib/bare-os/extensions/foo.js"] }`.
  * @param {Record<string, unknown>} ctx
@@ -2696,6 +2739,11 @@ async function runKernelExtDropins(ctx, opts = {}) {
           'kernelExt.denyId',
           `[kernel.ext.d] denied by policy id: ${extId}`
         )
+        await appendKernelExtAuditNdjson(ctx, {
+          event: 'deny_id',
+          extId,
+          dropin: name
+        })
         continue
       }
       const scripts = pol.scripts
@@ -2786,7 +2834,14 @@ async function runKernelExtDropins(ctx, opts = {}) {
           'kernelExt.conflict',
           `[kernel.ext.d] conflict: extension "${e.extId}" conflictsWith "${c}"`
         )
-        if (strictPol) return false
+        if (strictPol) {
+          await appendKernelExtAuditNdjson(ctx, {
+            event: 'conflict',
+            extId: e.extId,
+            conflictsWith: c
+          })
+          return false
+        }
       }
     }
   }
@@ -2813,7 +2868,13 @@ async function runKernelExtDropins(ctx, opts = {}) {
       '[kernel.ext.d] dependency cycle in extension drop-ins; ext ids: ' +
         topo.cycleExtIds.join(', ')
     )
-    if (strictPol) return false
+    if (strictPol) {
+      await appendKernelExtAuditNdjson(ctx, {
+        event: 'dependency_cycle',
+        cycleExtIds: [...topo.cycleExtIds].sort()
+      })
+      return false
+    }
     ordered = [...collected].sort((a, b) => a.file.localeCompare(b.file))
   } else {
     ordered = topo.ordered
@@ -3274,9 +3335,12 @@ async function maybeWriteBootPerfJson(ctx, bootT0, stageLog) {
       : undefined
   let schema = stages ? 2 : 1
   if (stdlibWall != null || stdlibBudget != null) schema = Math.max(schema, 3)
+  schema = Math.max(schema, 4)
   const row =
     JSON.stringify({
       schema,
+      bootGraphJsonPath: '/proc/bare_os/boot_graph.json',
+      stageLogSnapshot: [...stageLog],
       coldWallMs: wall,
       bootBudgetMsCold: budget,
       withinBudget: budget == null ? null : wall <= budget,
@@ -3492,7 +3556,10 @@ async function start(ctx) {
   } else {
     stageLog.push('rc.profile(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   if (!shouldSkipBootStage(ctx, 'rc')) {
     await bootTimed(
       ctx,
@@ -3505,7 +3572,10 @@ async function start(ctx) {
   } else {
     stageLog.push('rc(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   if (!shouldSkipBootStage(ctx, 'rc.d')) {
     await bootTimed(
       ctx,
@@ -3518,7 +3588,10 @@ async function start(ctx) {
   } else {
     stageLog.push('rc.d(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   if (!shouldSkipBootStage(ctx, 'rc.local')) {
     await bootTimed(
       ctx,
@@ -3531,7 +3604,10 @@ async function start(ctx) {
   } else {
     stageLog.push('rc.local(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   if (!shouldSkipBootStage(ctx, 'kernel.d')) {
     await bootTimed(
       ctx,
@@ -3544,7 +3620,10 @@ async function start(ctx) {
   } else {
     stageLog.push('kernel.d(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   if (!shouldSkipBootStage(ctx, 'kernel.ext.d')) {
     await bootTimed(
       ctx,
@@ -3557,7 +3636,10 @@ async function start(ctx) {
   } else {
     stageLog.push('kernel.ext.d(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   await bootTimed(
     ctx,
     'banner',
@@ -3578,7 +3660,10 @@ async function start(ctx) {
   } else {
     stageLog.push('onboot(skipped)')
   }
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   await bootTimed(
     ctx,
     'selftest',
@@ -3587,7 +3672,10 @@ async function start(ctx) {
     },
     stageLog
   )
-  if (!bootOk) return
+  if (!bootOk) {
+    await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
+    return
+  }
   publishBootReady(ctx, stageLog)
   await maybeWriteBootPerfJson(ctx, bootT0, stageLog)
   if (kernelExtHotReloadEnabled(ctx)) {