Three install.ps1 improvements pulled from the thin-installer work on
bb/gui (PR #27822) that benefit the canonical CLI install flow on main:
1. Strip UTF-8 BOM from scripts/install.ps1.
The canonical 'irm <raw URL> | iex' install flow has been broken
since commit 4279da4db re-introduced a UTF-8 BOM that PR #27224
had explicitly stripped. PowerShell 5.1's 'irm' returns the
response body as a string with the BOM surviving as a leading
\ufeff character; 'iex' then evaluates that string and the parser
chokes on the invisible character before param(), surfacing as a
cascade of 'The assignment expression is not valid' errors at
every param default value.
File body is verified pure ASCII (no character above byte 127),
so PS 5.1 with no BOM falls back to Windows-1252 decoding which
is identical to ASCII for our content. Both install paths work:
- 'irm ... | iex' (canonical one-liner)
- 'powershell -File install.ps1' (programmatic / desktop bootstrap)
2. New -Commit and -Tag string params for reproducible pinning.
Higher-precedence variants of -Branch. When set, the repository
stage clones $Branch (fast partial fetch) and then 'git checkout's
the exact ref. Precedence: Commit > Tag > Branch. Honoured by all
three code paths:
- Update path (existing valid checkout): fetch + checkout
--detach <commit|tag> instead of checkout + pull.
- Fresh clone: clone --branch $Branch, then post-clone
'git checkout --detach' to the requested ref.
- ZIP fallback: pick archive URL for the most-specific ref
(commit -> archive/<sha>.zip, tag -> archive/refs/tags/
<tag>.zip, else archive/refs/heads/<branch>.zip).
Used by the Hermes desktop's first-launch bootstrap to pin the
.exe to the exact commit it was built against, so the cloned
Hermes Agent tree always matches what the .exe was tested with.
Also enables release-bundle pinning (e.g. Microsoft Store builds
pinning to a release tag) and CI reproducibility.
3. EAP=Continue wrap around the new pin-step git invocations.
'git fetch origin <commit>' writes the routine 'From <url>' info
line to stderr. Under the script's global $ErrorActionPreference
= 'Stop' that stderr line is wrapped as an ErrorRecord and
terminates the script even though fetch+checkout actually succeed.
Same EAP=Stop + native-stderr footgun we hit during the install.ps1
hardening pass in Install-Uv, Test-Python, _Run-NpmInstall.
Wrap both the update-path fetch/checkout block AND the post-clone
pin block in $ErrorActionPreference = 'Continue' (restored in
finally). Real failures still caught by $LASTEXITCODE checks.
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