From a554db0fb469842df8df6d44d93984e6fe41bdb7 Mon Sep 17 00:00:00 2001
From: Kurt Himebauch <136133082+xXJSONDeruloXx@users.noreply.github.com>
Date: Sun, 4 Oct 2026 20:15:24 -0400
Subject: [PATCH] docs: record Thor Steam SD allocation findings (#240)

---
 .../evidence/thor-sd-storage-2026-10-04.txt   | 107 +++++
 docs/development/proot-performance.md         |   5 +
 .../thor-sd-storage-investigation.md          | 379 ++++++++++++++++++
 3 files changed, 491 insertions(+)
 create mode 100644 docs/development/evidence/thor-sd-storage-2026-10-04.txt
 create mode 100644 docs/development/thor-sd-storage-investigation.md

diff --git a/docs/development/evidence/thor-sd-storage-2026-10-04.txt b/docs/development/evidence/thor-sd-storage-2026-10-04.txt
new file mode 100644
index 000000000..17961978f
--- /dev/null
+++ b/docs/development/evidence/thor-sd-storage-2026-10-04.txt
@@ -0,0 +1,107 @@
+Thor SD storage investigation: selected saved evidence
+Recorded 2026-10-04; event timestamps are EDT.
+These are excerpts, not complete logs or a continuous attribution profile.
+See ../thor-sd-storage-investigation.md for context and live-only observations.
+
+=== Reporter unsupported allocation ===
+Source: Reporter diagnostic storage.log
+volume_removable=true
+filesystem=fuse
+allocation pid=29062 comm=steam api=fallocate result=-1 api_error=95 errno_after=95 flags=0x0 offset=0 length=374272 elapsed_us=212
+
+=== Thor unsupported allocation ===
+Source: candidate-storage.log
+volume_removable=true
+filesystem=fuse
+allocation pid=9810 comm=steam api=fallocate result=-1 api_error=95 errno_after=95 flags=0x0 offset=0 length=650752 elapsed_us=310
+
+=== Native-path allocation diagnostics ===
+Source: direct-storage-completed.log / session 64
+DroidDeck storage diagnostics v1
+selected_library=secondary
+volume_removable=true
+filesystem=exfat
+truncate_allocation_probe=passed
+block_size_bytes=131072
+total_bytes=393855500288
+available_bytes=101076697088
+native_observation=enabled
+public_symbol_interposition=enabled
+direct_syscalls_and_libc_internal_calls=not_observed
+pwrite_timing=sampled_1_in_32
+per_process_allocation_detail_limit=64
+storage_log_limit_bytes=524288
+summary pid=26725 comm=python3 allocation_calls=0 allocation_failures=0 allocation_total_us=0 pwrite_sample_every=32 pwrite_samples=0 pwrite_bytes=0 pwrite_failures=0 pwrite_sample_total_us=0 pwrite_sample_max_us=0 ftruncate_calls=0 ftruncate_failures=0 ftruncate_total_us=0 ftruncate_max_us=0 fstat_calls=1 fstat_total_us=0 fstat_max_us=0 fsync_calls=0 fsync_failures=0 fsync_total_us=0 fsync_max_us=0
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=667648 elapsed_us=387
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=39 elapsed_us=32
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=156 elapsed_us=25
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=457428 elapsed_us=351
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=901928 elapsed_us=864
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=15041920 elapsed_us=15292
+allocation pid=26825 comm=steam api=fallocate_ftruncate result=0 api_error=0 errno_after=0 flags=0x0 offset=0 length=337563 elapsed_us=2783
+
+=== Fresh real Steam install ===
+Source: direct-content-completed.log / session 64
+[2026-10-04 17:31:20] AppID 1675830 App update changed : Running Update,Preallocating,
+[2026-10-04 17:38:04] AppID 1675830 preallocated 2216 files (7626 MB)
+[2026-10-04 17:38:06] AppID 1675830 App update changed : Running Update,Downloading,Staging,
+[2026-10-04 17:45:25] AppID 1675830 App update changed : Running Update,Committing,
+[2026-10-04 17:45:25] AppID 1675830 starting commit from "/mnt/droiddeck-sd/steamapps/downloading/1675830" to "/mnt/droiddeck-sd/steamapps/common/1000xRESIST" : 2230 updated, 0 moved, 0 deleted files
+[2026-10-04 17:47:55] AppID 1675830 state changed : Fully Installed,Update Queued,Update Running,
+[2026-10-04 17:47:55] AppID 1675830 finished update, 1 mounted depots (BuildID 21498291) : 1675831 (3663189783241284849),
+[2026-10-04 17:47:56] AppID 1675830 state changed : Fully Installed,Update Queued,
+[2026-10-04 17:47:56] AppID 1675830 state changed : Fully Installed,
+[2026-10-04 17:47:56] AppID 1675830 scheduler finished : removed from schedule (result No Error, state 0xc)
+
+=== Normal-app native/FUSE directory read ===
+Source: app-raw-probe-session.log / session 62
+APP_RAW_PROBE uid=10195 path=/mnt/media_rw/FF7F-F56A/Android/data/com.droiddeck.launcher/files/steam/steamapps/downloading/1675830-fuse-control/1000xRESIST_Data/StreamingAssets/aa/StandaloneWindows64 seconds=0.002288 calls=2 bytes=154920 read_error=0
+APP_RAW_PROBE uid=10195 path=/storage/FF7F-F56A/Android/data/com.droiddeck.launcher/files/steam/steamapps/downloading/1675830-fuse-control/1000xRESIST_Data/StreamingAssets/aa/StandaloneWindows64 seconds=0.501306 calls=112 bytes=154872 read_error=0
+
+=== Binding regression: bind-probe-before.log ===
+Source: bind-probe-before.log
+BIND_PROBE index=0 pass=1 errno=0 bytes=17 path=/mnt/droiddeck-sd/steamapps/common/SteamLinuxRuntime_4-arm64/.droiddeck-bind-probe
+BIND_PROBE index=1 pass=1 errno=0 bytes=17 path=/mnt/droiddeck-sd/steamapps/common/steamlinuxruntime_4-arm64/.droiddeck-bind-probe
+BIND_PROBE index=2 pass=0 errno=2 bytes=-1 path=/mnt/droiddeck-sd/steamapps/common/proton experimental (arm64)/.droiddeck-bind-probe
+BIND_PROBE index=3 pass=0 errno=2 bytes=-1 path=/mnt/bannerlator-sd/steamapps/shadercache/.droiddeck-bind-probe
+
+=== Binding regression: bind-probe-after.log ===
+Source: bind-probe-after.log
+BIND_PROBE index=0 pass=1 errno=0 bytes=17 path=/mnt/droiddeck-sd/steamapps/common/SteamLinuxRuntime_4-arm64/.droiddeck-bind-probe
+BIND_PROBE index=1 pass=1 errno=0 bytes=17 path=/mnt/droiddeck-sd/steamapps/common/steamlinuxruntime_4-arm64/.droiddeck-bind-probe
+BIND_PROBE index=2 pass=1 errno=0 bytes=17 path=/mnt/droiddeck-sd/steamapps/common/proton experimental (arm64)/.droiddeck-bind-probe
+BIND_PROBE index=3 pass=1 errno=0 bytes=17 path=/mnt/bannerlator-sd/steamapps/shadercache/.droiddeck-bind-probe
+
+=== Root metadata/mount experiment: metadata-mount-comparison.log ===
+Source: metadata-mount-comparison.log
+original_mount
+/dev/block/vold/public:179,1 /mnt/media_rw/FF7F-F56A exfat rw,dirsync,nosuid,nodev,noexec,noatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,iocharset=utf8,errors=remount-ro 0 0
+files=64 bytes_per_file=262144 open_seconds=6.707435 truncate_seconds=0.084806 wall_seconds=6.794807 error=0
+mount: '/dev/block/vold/public:179,1'->'/mnt/media_rw/FF7F-F56A': Invalid argument
+mount: '/dev/block/vold/public:179,1'->'/mnt/media_rw/FF7F-F56A': Invalid argument
+
+=== Root metadata/mount experiment: metadata-syscall-comparison.log ===
+Source: metadata-syscall-comparison.log
+original_mount
+/dev/block/vold/public:179,1 /mnt/media_rw/FF7F-F56A exfat rw,dirsync,nosuid,nodev,noexec,noatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,iocharset=utf8,errors=remount-ro 0 0
+files=64 bytes_per_file=262144 open_seconds=25.181255 truncate_seconds=0.309577 wall_seconds=25.493210 error=0
+temporary_mount
+/dev/block/vold/public:179,1 /mnt/media_rw/FF7F-F56A exfat rw,dirsync,nosuid,nodev,noexec,noatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,iocharset=utf8,errors=remount-ro 0 0
+files=64 bytes_per_file=262144 open_seconds=2.013194 truncate_seconds=0.095924 wall_seconds=2.112288 error=0
+
+=== Post-install Android low-memory exit ===
+Source: game-launch-exit-info.txt
+        ApplicationExitInfo #0:
+          timestamp=2026-10-04 18:13:48.454 pid=14709 realUid=10195 packageUid=10195 definingUid=10195 user=0
+          process=com.droiddeck.launcher reason=3 (LOW_MEMORY) subreason=0 (UNKNOWN) status=0
+          importance=100 pss=227MB rss=344MB description=null state=empty trace=null
+
+=== Combined release unit-test completion ===
+Source: combined-233-tests.log
+> Task :app:testReleaseUnitTest
+BUILD SUCCESSFUL in 10s
+
+=== Combined release build completion ===
+Source: combined-233-build.log
+BUILD SUCCESSFUL in 25s
+APK: /Users/danhimebauch/.codex/worktrees/steam-sd-preallocation/DroidDeck/app/build/outputs/apk/release/app-release.apk
diff --git a/docs/development/proot-performance.md b/docs/development/proot-performance.md
index e9f18847b..3679f43ea 100644
--- a/docs/development/proot-performance.md
+++ b/docs/development/proot-performance.md
@@ -5,6 +5,11 @@ games should keep running under proot, run directly on glibc, or a mix of the tw
 fastest correct setup is. Everything below was measured on a Snapdragon 8 Elite Gen 5 (SM8850, kernel
 6.12.38-android16, Android 16) over adb, unless it says otherwise.
 
+For Steam SD allocation measurements on AYN Thor (Android 13), see the
+[Thor storage investigation](thor-sd-storage-investigation.md). It separates
+observed allocation-wrapper time, FUSE directory access and native exFAT metadata
+waits; it does not establish a full-install PRoot overhead percentage.
+
 ## Short answer
 
 - **Don't drop proot.** On Android it does two jobs. It translates paths. It also answers every
diff --git a/docs/development/thor-sd-storage-investigation.md b/docs/development/thor-sd-storage-investigation.md
new file mode 100644
index 000000000..b2cfbce55
--- /dev/null
+++ b/docs/development/thor-sd-storage-investigation.md
@@ -0,0 +1,379 @@
+# Steam SD allocation on Thor
+
+Investigation recorded on 2026-10-04. Device measurements and PR states below are a
+snapshot of that day's work. All event times are EDT (UTC−04:00).
+
+A fresh 1000xRESIST install on the Thor SD card completed with the native-path and
+allocation-fallback patches: 2,216 files preallocated in **6m44s**, followed by a
+successful download and commit, **16m36s total**. The observed allocation wrappers
+reported zero failures and roughly 7.1 seconds of aggregate execution time.
+That wrapper measurement does **not** account for the entire preallocation phase.
+
+Native directory access was substantially faster than Android's FUSE view in a
+small controlled probe. Kernel samples during the remaining delay showed exFAT
+file-creation and size-update waits. This supports further investigation of SD
+metadata writes. It does not establish that PRoot is free, that `dirsync` alone
+causes the delay, or that SD now matches internal-storage install speed.
+
+Selected source-log excerpts are preserved in
+[the evidence file](evidence/thor-sd-storage-2026-10-04.txt). The original full logs
+contain unrelated sessions and are not needed to interpret those excerpts.
+
+## Device and storage
+
+| Item | Observed configuration |
+|---|---|
+| Device | AYN Thor, Android 13, kernel 5.15.123, 12 GB RAM and 8 GB swap |
+| App | Production-signed `com.droiddeck.launcher`, normal app UID 10195 |
+| Configured SD library | `/storage/FF7F-F56A/Android/data/com.droiddeck.launcher/files/steam` |
+| Native view of the same library | `/mnt/media_rw/FF7F-F56A/Android/data/com.droiddeck.launcher/files/steam` |
+| Guest content aliases | `/mnt/droiddeck-sd` and legacy `/mnt/bannerlator-sd` |
+| SD filesystem | Native exFAT; its Android `/storage` view reports FUSE |
+| Native filesystem magic | `0x2011BAB0`, matching the NDK Linux header |
+| Internal comparison location | App-private cache under `/data` |
+
+The native SD mount was observed with these options:
+
+```text
+rw,dirsync,nosuid,nodev,noexec,noatime,uid=1023,gid=1023,fmask=0007,dmask=0007,allow_utime=0020,iocharset=utf8,errors=remount-ro
+```
+
+The device already had root and SELinux Permissive. Neither state was introduced
+by this investigation. Root was used for inspection and temporary experiments.
+The validated Steam session ran with the app's normal UID and existing groups,
+without a root launcher or an app-specific Magisk root grant.
+
+This distinction does not prove the native path works on an unrooted device with
+enforcing SELinux. The production change tests access in the app and retains the
+configured path when verification fails.
+
+## Initial report and allocation failure
+
+The [linked Discord report](https://discord.com/channels/1552707793247539220/1555632840388116491/1556271955076710560)
+included a newer diagnostic ZIP with `storage.log`. Unlike the earlier capture
+that lacked allocation instrumentation, this capture established:
+
+- The selected secondary library was removable and its exposed filesystem was
+  FUSE.
+- Steam called mode-zero `fallocate` and received `EOPNOTSUPP` (errno 95).
+- That observed failure returned in 212 microseconds. It was not itself a
+  multi-minute blocked call.
+
+A Thor baseline capture likewise showed `fallocate` failing with errno 95 in
+310 microseconds. These establish an unsupported allocation API on the tested
+paths. They do not attribute the later Steam delay to any particular fallback.
+
+The suggestion that glibc's `posix_fallocate` emulation accounts for the whole
+hang was not established by those logs. The tested Steam calls included
+`fallocate`; directory operations and other calls occur outside that wrapper.
+
+## Published patches and the tested build
+
+The main base was `26cb9e2f038cdbab4cdc8670d2f64c18d1d90875`. These heads were
+checked again while preparing this report; all three storage PRs were open with
+successful Build APK checks and clean merge states. This is a dated snapshot,
+not a statement about their future merge status.
+
+| PR | Tested head | Behavior |
+|---|---|---|
+| [#221](https://github.com/Droid-Deck/DroidDeck/pull/221) | `7962c19283bfb0f18a5c7672e08a879814a3d5a1` | Verify a native SD content alias and handle safe case aliases in the path fast path |
+| [#229](https://github.com/Droid-Deck/DroidDeck/pull/229) | `4628ae4c92cc5813013537165a0e95886e6de904` | Use a verified truncate fallback for unsupported selected-library allocation |
+| [#233](https://github.com/Droid-Deck/DroidDeck/pull/233) | `5c6765233ae5405d7bd4c1b29f20c9e8343a1fed` | Preserve the complete fast-path binding table, including later private overrides |
+| [#225](https://github.com/Droid-Deck/DroidDeck/pull/225) | `0b5908d6d63080f625b51bab3439e2e68466631e` | Repair repeated failed Steam client starts; reviewed separately, excluded from this storage build |
+
+### Native content path and case handling: #221
+
+For a configured `/storage/...` library, the launcher checks the corresponding
+`/mnt/media_rw/...` candidate. It requires usable directory permissions and
+performs a write/read/delete identity probe through both views. Failure keeps
+the original configured path.
+
+Only the shared SD content bindings change. The configured path remains the
+library's identity for private prefixes, migrations and other private storage.
+This avoids moving existing saves or runtime state when selecting a faster view.
+Removable-volume detection also uses the original configured path because
+Android's volume API need not recognize the native alias.
+
+The C fast path permits case-only canonical-parent differences on known
+FUSE/FAT/exFAT filesystems only after checking directory components without
+following symlinks. It also handles the supported `F_OK` plus
+`AT_SYMLINK_NOFOLLOW` case. Ambiguous paths still fall back to PRoot.
+
+The final #221 diff was four files, 98 insertions and 20 deletions, including
+28 new test lines. The experimental directory cache was removed from that diff.
+
+### Allocation fallback: #229
+
+The launcher first creates a temporary 1 MiB file on the selected content path,
+extends it, and checks that `st_blocks` reports at least 2,048 512-byte blocks.
+The file must also be cleaned up successfully. The fallback is enabled only for
+a removable library that passes this reservation probe.
+
+For file descriptors on the selected library device, the wrapper tries the real
+allocation API. On mode-zero `fallocate` returning `EOPNOTSUPP`, it extends the
+file with `ftruncate`. It validates the range, detects overflow and avoids
+shrinking an existing file. Other modes and other errors retain their normal
+behavior. The POSIX wrapper tries kernel allocation first to avoid unnecessary
+libc emulation and preserves POSIX error-return and `errno` semantics.
+
+This is a capability-tested fallback, not unconditional successful allocation
+reporting. A failed extension still returns an error. The optimization operates
+independently of the optional diagnostic toggle.
+
+The reservation probe and one successful full install do not replace separate
+future tests for ENOSPC, interrupted installs or other devices/filesystems.
+
+### Complete binding table: #233
+
+The real Steam session had **96 bindings**. The old C limit of 64 silently
+dropped later mappings. Several of those were private overrides inside the
+shared SD root, so truncation could send an operation to the wrong location or
+return `ENOENT`.
+
+#233 raises capacity to 256 and makes both the launcher and C implementation
+disable the fast path if a complete table cannot be represented. Overlong paths
+also cause fallback rather than partial mapping. This is a correctness fix as
+well as a requirement for trusting the storage fast path.
+
+Marker files existed only in private directories. A normal app-process probe
+read them through these guest paths:
+
+| Guest path under the library | Before #233 | After #233 |
+|---|---|---|
+| `SteamLinuxRuntime_4-arm64` | Correct private marker | Correct private marker |
+| `steamlinuxruntime_4-arm64` | Correct private marker | Correct private marker |
+| `proton experimental (arm64)` | `ENOENT` | Correct private marker |
+| Legacy `steamapps/shadercache` | `ENOENT` | Correct private marker |
+
+Each successful read returned the 17-byte `private-override\n` marker. The
+temporary markers and helper executable were removed afterward.
+
+### Deployment and checks
+
+The full fresh install used #221 plus #229. #233 was then integrated locally,
+tested, built and installed for the binding regression and game-launch check.
+It was not merged on GitHub during this investigation.
+
+The combined integration commit was
+`f5d3e93b8eb8912ca3834f7447a6498c95250177`. The production-signed APK was installed
+in place with `adb install -r`; its SHA-256 was:
+
+```text
+099a0d7e76b9462b3b238c6f1abeb03570ec9708ace3092adf178ec2bee63e2a
+```
+
+`tools/build_local.sh` completed for the combined build. The release unit tests
+for `SecondaryLibraryTest` and `ProotFastPathTest` passed. The latter covers
+96/256 bindings, exceeding capacity, and overlong paths. #225 was reviewed for
+scope; its tests were not run as part of this storage validation.
+
+## Fresh real Steam install
+
+Game: **1000xRESIST**, app 1675830, depot 1675831, BuildID 21498291. Steam reported
+6,582,351,824 download bytes and 7,997,085,707 staging bytes, approximately 8 GB.
+
+| Event | Time | Evidence |
+|---|---|---|
+| Fresh preallocation began | 17:31:20 | Steam entered `Preallocating` |
+| Preallocation completed | 17:38:04 | 2,216 files, 7,626 MB in Steam's log |
+| Download/staging began | 17:38:06 | `Downloading,Staging` |
+| Commit began | 17:45:25 | 2,230 updated files |
+| Fully installed | 17:47:55 | `Fully Installed`, BuildID 21498291 |
+| Scheduler completed | 17:47:56 | `No Error` |
+
+Preallocation took **404 seconds**. Start to scheduler completion took
+**996 seconds**. Live counters showed 2,216 allocation calls, zero allocation
+failures and about **7.1 seconds aggregate allocation-wrapper time**. The saved
+diagnostic detail log is capped at the first 64 allocation details per process;
+that file alone cannot reproduce the live aggregate counter observation.
+
+The final manifest had `StateFlags=4`, `UpdateResult=0`, all expected download
+and staging bytes completed, and `SizeOnDisk=7997085707`. The completed executable
+was under `steamapps/common/1000xRESIST`; the active staging directory was gone.
+
+Transfer rates were mostly 117–132 Mbps, about 15–16.5 MB/s. Two root metadata
+experiments ran during downloading, so this is not a clean network/card
+throughput benchmark. No matched full internal-storage install was performed.
+
+The run's `storage.log` reported native exFAT and a passed truncate reservation
+probe. Recorded allocation details used `api=fallocate_ftruncate`, with
+`result=0` and `api_error=0`.
+
+## What the metadata measurements show
+
+Metadata is filesystem bookkeeping: names, directory entries, sizes and space
+allocation. Steam's `Preallocating` phase includes work outside the observed
+allocation wrappers, including creating and locating files.
+
+### Directory reads through native and FUSE paths
+
+A helper ran in a normal app process and listed the same stable asset directory
+from a saved staging tree through both host paths. It used the existing fast-path
+syscall trampoline to bypass PRoot path translation while retaining the app's
+Android permissions. The read buffer was 128 KiB.
+
+| View | Elapsed | Successful `getdents64` calls | Directory bytes |
+|---|---|---|---|
+| Native exFAT | About 2.3 ms | 2 | 154,920 |
+| Android FUSE | About 501 ms | 112 | 154,872 |
+
+The views returned slightly different byte counts. This was a single
+native-first pass, not a repeated benchmark with fully controlled cache state.
+It demonstrates a large cost difference for that directory read, not a
+corresponding multiplier for a full Steam install.
+
+An earlier root listing during concurrent file creation measured roughly
+5.56 seconds through FUSE and 9.25 milliseconds native. Its directory was
+changing, so it is weaker evidence and is not used as a controlled comparison.
+
+### File creation and size updates
+
+During the fresh native-path Steam run, sampled kernel stacks included:
+
+```text
+__sync_dirty_buffer -> exfat_update_bh -> exfat_init_ext_entry
+    -> exfat_add_entry -> exfat_create -> path_openat
+
+__wait_on_buffer -> exfat_update_bhs -> exfat_free_dentry_set
+    -> __exfat_write_inode -> exfat_truncate -> do_sys_ftruncate
+```
+
+These were live samples, not a continuous attribution profile. They show time
+waiting in the native filesystem's creation/update paths during the delay.
+
+A root-only helper created a temporary directory, then 64 long-named files using
+`open(O_CREAT|O_EXCL|O_WRONLY, 0600)`, `ftruncate(fd, 262144)` and `close`. It timed
+the creation and truncate calls separately and removed its files afterward.
+
+| Location/run | Sum of open times | Sum of truncate times | Whole loop |
+|---|---|---|---|
+| Native SD, original mount | 6.707435 s | 0.084806 s | 6.794807 s |
+| Native SD, later repeat | 25.181255 s | 0.309577 s | 25.493210 s |
+| Internal app cache, live observation | About 7.88 ms | About 0.498 ms | About 9.1 ms |
+
+The SD results varied substantially, and these root probes do not reproduce the
+normal app's complete Steam workload. The measured internal probe is not a full
+internal-install benchmark. Within these probes, file creation cost far more
+than the observed truncate calls.
+
+### `dirsync` and the failed remount comparison
+
+The [Linux mount documentation](https://man7.org/linux/man-pages/man2/mount.2.html)
+defines `MS_DIRSYNC` as synchronous directory changes. Combined with the observed
+exFAT buffer waits, this makes synchronous SD metadata updates a strong lead.
+It remains an inference about the remaining overall delay.
+
+A toybox remount attempt returned `Invalid argument`. A direct mount-syscall
+experiment changed the root view, but Steam's observed mount table still showed
+`dirsync`. A subsequent 64-file probe took 2.112288 seconds; because the effective
+flag change was not established and timings were variable, this is **not proof
+that removing `dirsync` improves Steam allocation**. The Linux documentation also
+notes that attempts to change `MS_DIRSYNC` during a remount are silently ignored.
+
+Original effective options were restored and checked in root and app/process
+views. No remount or root-launch behavior is included in the production patches.
+
+### What remains attributable to PRoot
+
+One sampled Steam worker was executing an `openat` through the fast-path
+trampoline at `0xffff00020`, with an absolute native host path. That establishes
+that some operations bypassed PRoot's path translation in the actual session.
+Other syscalls still use PRoot.
+
+There was no matched PRoot-versus-direct full preallocation comparison. The
+fraction of the 404 seconds attributable to PRoot is therefore unknown. The
+earlier [PRoot performance notes](proot-performance.md) concern different hardware
+and workloads and cannot supply that missing percentage.
+
+Seven seconds in public allocation wrappers does not mean the remaining
+397 seconds are unrelated to allocation: libc-internal/direct-syscall bypasses,
+explicit size changes and file-creation work may occur outside those counters.
+
+## Experiments that did not become the fix
+
+- **Directory caching:** eager scans held up directory open; creation-driven
+  invalidation repeatedly reread growing directories. The capped design could
+  also read and discard a large directory before rereading it. A lazy variant
+  still left 182 files taking 4m49s while the allocation wrappers accounted for
+  only 0.879 seconds. These were interrupted/resumed runs, not a matched A/B
+  benchmark. The final #221 snapshot removes the cache entirely.
+- **Allocation fallback alone:** a FUSE-path attempt was still slow after
+  unsupported allocation calls were handled. A later eager-cache resumed run
+  accumulated roughly 8.36 seconds in 1,435 successful allocation calls over
+  about 36 minutes of wall time. Successful wrappers alone were insufficient.
+- **Launching Steam through root:** experimental wrappers failed compositor
+  startup. They did not produce allocation measurements and were reverted.
+- **Changing mount flags:** effective removal of `dirsync` from Steam's view was
+  not demonstrated. The apparent probe speedup is not a validated fix.
+- **Replacing PRoot or reformatting storage:** no such replacement, adoptable
+  storage conversion or ext4 loop-image deployment was validated here.
+
+The early FUSE runs used partial staging state. Their file counts and durations
+must not be compared to the fresh 2,216-file run as a precise speedup ratio.
+
+## Post-install launch and separate memory failure
+
+After deploying #221 + #229 + #233, the installed SD game was launched through
+Steam. First-run Proton prefix initialization preceded the game window.
+
+At **18:10:45**, the compositor changed from Steam Big Picture to **1000xRESIST**
+and received the game's 1280×720 GPU frames. A screenshot showed the game loading
+screen and spinner. A main menu or sustained gameplay was not validated.
+
+At **18:13:48.454**, Android recorded the foreground app's exit as reason 3,
+`LOW_MEMORY`, with main-app PSS 227 MB and RSS 344 MB. Those figures describe that
+process, not the complete native process tree or its peak memory use. Subsequent
+gamescope/reaper shutdown messages followed the parent being killed.
+
+This was after the install had completed. It is a separate unresolved launch/
+memory issue and does not undo the successful allocation/download result.
+Post-kill free-memory readings cannot establish peak memory pressure.
+
+## Remaining questions and next useful tests
+
+1. Run the same fresh game install on internal and secondary storage with the
+   same manifest, awake device and no competing benchmarks. Compare preallocation,
+   download/staging and commit separately.
+2. Match the file-creation/extension workload through PRoot and through the normal
+   app's direct syscall path. Keep UID, filesystem, names and sizes identical,
+   repeat runs and record background I/O. This can quantify the remaining tracer
+   contribution without changing storage semantics.
+3. Establish an actual controlled difference in synchronous directory behavior
+   before attributing a speedup to mount flags. A remount return code alone is
+   insufficient; this is separate from a portable app patch.
+4. Validate native-path fallback under enforcing SELinux and on unrooted devices,
+   plus allocation behavior near ENOSPC and after interruption. Preserve the
+   configured-path fallback if either access or reservation verification fails.
+5. Investigate the low-memory exit with process-tree/cgroup memory and Android
+   kill evidence during loading. Treat it separately from install performance.
+
+At this point, one fresh SD install and the binding regression are validated.
+Internal-speed parity, the exact PRoot share, a `dirsync` remedy, broad device
+coverage and stable gameplay remain unproven.
+
+## Evidence inventory and handoff state
+
+The device captures used for the final measurements were:
+
+- `2026-10-04-62-app-raw-probe`: normal-app native/FUSE directory probe.
+- `2026-10-04-64-steam`: fresh complete allocation/download/commit.
+- Probe sessions before and after #233: private binding markers.
+- `2026-10-04-67-steam`: combined-build launch, followed by Android's low-memory
+  kill; the exit reason was obtained separately with `dumpsys activity exit-info`.
+
+Local originals during the investigation were under
+`/tmp/droiddeck-storage-live/`: `direct-content-completed.log`,
+`direct-storage-completed.log`, `app-raw-probe-session.log`,
+`bind-probe-before.log`, `bind-probe-after.log`,
+`metadata-mount-comparison.log`, `metadata-syscall-comparison.log`,
+`game-launch-exit-info.txt`, `combined-233-build.log` and
+`combined-233-tests.log`. The repository evidence file preserves the selected
+excerpts even if those temporary local files disappear. Live-only counters,
+kernel samples and the internal metadata timing are identified above rather
+than represented as saved continuous traces.
+
+The combined signed build and completed SD install remained on Thor. Storage
+diagnostics remained enabled. Temporary probe files, executables and obsolete
+partial staging were removed after validation. Original effective mount options
+were restored; no app-specific Magisk root policy remained. The primary checkout's
+unrelated `SessionService.kt` modification was preserved.