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claudetools/clients/cascades-tucson/session-logs/2026-06/2026-06-08-howard-edge-unc-download-bug-diagnosis.md
Howard Enos 7a84b30047 sync: auto-sync from HOWARD-HOME at 2026-06-08 15:25:56 
Author: Howard Enos
Machine: HOWARD-HOME
Timestamp: 2026-06-08 15:25:56
2026-06-08 15:26:05 -07:00

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Cascades of Tucson — Session Log 2026-06-08 — Edge UNC Download Bug Diagnosis

User

  • User: Howard Enos (howard)
  • Machine: Howard-Home
  • Role: tech

Session Summary

Diagnosed (no changes made) a user-reported issue at Cascades: Ashley Jensen (DESKTOP-U2DHAP0, domain-joined, Downloads folder redirected to the \\cs-server\homes UNC share) could not open Office downloads from the Microsoft Edge download list. Clicking a downloaded .xlsx/.docx in Edge produced "Windows cannot find '\?\\cs-server\homes\AshleyJensen\Downloads<file>'." Text files and PDFs opened fine from the same Edge action; the same Office files opened fine when double-clicked from File Explorer. Howard wanted root cause first, not a fix.

Worked the symptom to a root cause: the \\?\ is the Win32 extended-length path prefix, and the error path is the malformed result of prepending \\?\ to a UNC path (\\?\ + \\cs-server = \\?\\\cs-server) instead of the correct \\?\UNC\cs-server\.... Confirmed with Howard's test that Explorer double-click works and only the Edge download-list "open" fails — isolating the fault to Edge's open-from-download invocation, not the file, share, or folder redirection.

Howard found and supplied the canonical upstream bug: Chromium issue 519243472, "Can't open downloaded file when Downloads folder is a UNC path (malformed \\?\ path on open)" — Status Fixed, P0/S2, component UI>Browser>Downloads. The report confirms the exact mechanism: a regression introduced in Chromium 149 (last good 148.0.7778.217, first bad 149.0.7827.54) in the LaunchShellExecuteViaExplorer feature, which prepends \\?\ to a UNC path without converting to \\?\UNC\. Triggered specifically by Downloads redirected via Folder Redirection to a network UNC path with no mapped drive — exactly Ashley's configuration. The earlier "Open Office files in the browser" theory was retracted; that was not the cause.

Confirmed applicability to Cascades: Ashley and Lois Lane are on Edge 149.0.4022.52 (June 4, 2026 stable). Edge rides the Chromium 149 base, so it inherits the regression (the original reporter thought Edge was immune, but bug comment #27, dated 2026-06-08, confirms Edge affected in RDS/Citrix/AVD). The txt/pdf-work-Office-fails split is explained by only the external ShellExecute launch path being broken (PDF opens in Edge's built-in viewer; Office routes through the broken launch). Presented fix options ranked for the HIPAA environment: update Edge forward into the fix, the --disable-features=LaunchShellExecuteViaExplorer flag, "Show in folder" workaround, or a supported 149→148 MSI rollback. Howard asked about a simple "uninstall the update" rollback; clarified Edge is not serviced via Windows Update so no per-update revert exists — the MSI + RollbackToTargetVersion + version-pin is the only supported downgrade. No changes were applied this session; decision on fix path left to Howard.

Key Decisions

  • Diagnosed root cause before proposing any fix, per Howard's explicit "no changes, figure out the cause" instruction. Treated the Explorer-works / Edge-fails split as the key discriminator.
  • Retracted the intermediate "Open Office files in the browser" hypothesis once the Chromium bug report identified LaunchShellExecuteViaExplorer as the actual regression. Did not defend the earlier guess.
  • Recommended the lighter fixes (feature flag, wait for the fixed Edge 149.x, or "Show in folder") over a full version rollback for HIPAA machines, because pinning to 148 forfeits 149 security fixes and must be unwound later. Provided the full supported rollback procedure anyway since Howard requested it.
  • Flagged the issue as fleet-wide, not Ashley-specific: every Cascades user with Downloads redirected to the \\cs-server\homes UNC share will hit it once on Edge 149 (the whole domain-migrated set plus the caregiver/medtech machines using the same redirect pattern).

Problems Encountered

  • Could not fetch the Reddit thread or the Chromium tracker pages directly — Reddit is hard-blocked for WebFetch, and issues.chromium.org / issuetracker.google.com are JS apps behind sign-in that return only the login shell. Web search did not surface the specific issue. Resolved when Howard copy-pasted the full bug report text, which provided the authoritative root cause, regression range, and fix status.

Configuration Changes

  • None. Diagnostic-only session. No tenant, RMM, GPO, or repo config changed.
  • This session log created: clients/cascades-tucson/session-logs/2026-06/2026-06-08-howard-edge-unc-download-bug-diagnosis.md.

Credentials & Secrets

  • None discovered or created this session. (Separately this day, the Lonestar Electrical Unraid root password was read from the vault on request — entry clients/lonestar/unraid-server.sops.yaml; not a Cascades item, value not reproduced here.)

Infrastructure & Servers

  • Affected machines: DESKTOP-U2DHAP0 (Ashley Jensen), DESKTOP-KQSL232 (Lois Lane) — both on Edge 149.0.4022.52.
  • Redirect target: \\cs-server\homes\<user>\Downloads (CS-SERVER 192.168.2.254, file server / homes share D:\Homes). No mapped drive — raw UNC, which is the bug's required trigger.
  • Edge stable app GUID (for EdgeUpdate pin): {56EB18F8-B008-4CBD-B6D2-8C97FE7E9062}.

Commands & Outputs

  • Error dialog (verbatim from screenshot): Windows cannot find '\\?\\cs-server\homes\AshleyJensen\Downloads\Resident Demographics Table.xlsx'. Make sure you typed the name correctly, and then try again.
  • Discriminator test (Howard): double-click the same xlsx from File Explorer at \\cs-server\homes\AshleyJensen\Downloads → opens normally. Only the Edge download-list "open" fails.
  • Edge version check (Howard): Ashley + Lois both 149.0.4022.52.

Fix options (reference — none applied)

  1. Update Edge forward into the fixed build (permanent; Chromium fix crrev 7900033 "Correctly handle UNC paths in InvokeShellExecute", merged M149/M150, verified Chromium 151.0.7875.0). Re-enabled the feature after fixing, so the code fix — not a disabled flag — is the real resolution.
  2. Feature flag (interim): Edge shortcut target → "C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe" --disable-features=LaunchShellExecuteViaExplorer (fully quit Edge first; only applies to launches from that shortcut).
  3. "Show in folder" in the Edge download list → open from Explorer (zero-config; confirmed working).
  4. Supported 149→148 rollback (one major back is in-bounds):
    • Download 148 stable MSI from https://www.microsoft.com/en-us/edge/business/download (Stable / 148 / Win x64).
    • HKLM\SOFTWARE\Policies\Microsoft\Edge → RollbackToTargetVersion (DWORD) = 1 (set BEFORE install; enables downgrade + preserves profile).
    • HKLM\SOFTWARE\Policies\Microsoft\EdgeUpdate → TargetVersionPrefix{56EB18F8-B008-4CBD-B6D2-8C97FE7E9062} (REG_SZ) = 148. and Update{56EB18F8-...} (DWORD) = 2 (manual) (pins it; else auto-update returns to 149).
    • Install 148 MSI → verify edge://version = 148.x and edge://policy shows the rollback + target-prefix active.
    • Unwind later (RollbackToTargetVersion=0, remove TargetVersionPrefix) once a fixed Edge 149.x/150 ships.

Pending / Incomplete Tasks

  • Decision pending (Howard): pick fix path for Ashley + Lois — feature flag vs "Show in folder" vs 148 MSI rollback vs wait for fixed Edge 149.x. No changes made this session.
  • Fleet exposure: all Cascades users with Downloads redirected to \\cs-server\homes + Edge 149 will hit this (Sharon Edwards, Crystal Rodriguez, Lauren Hasselman, Megan Hiatt, receptionist/nursestation, and the caregiver/medtech machines). Decide whether to fix fleet-wide (lean flag/wait, not a fleet-wide 148 pin, to avoid holding the fleet off security updates).
  • Offered, not yet run: read-only RMM pull of Edge version + update channel across the Cascades agent fleet to quantify how many machines are on the affected 149 build.
  • Watch: Edge stable release notes for the servicing build that carries the InvokeShellExecute UNC fix; flag it so pinned/rolled-back machines can go forward.
  • Unrelated and still open from prior session: caregiver/medtech Monday go-live runbook (reboot/verify NURSESTATION lockdown, ALIS timeout 20→15, CA allow-list + GPO filter cutover, laptop hybrid-join gap).

Reference Information

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