* Verify linuxdeploy AppImage digest before use in desktop release
The desktop release workflow downloaded linuxdeploy-x86_64.AppImage from a
GitHub release and ran chmod +x with no integrity check. Pinning the
versioned release path is reproducibility, not integrity: a release asset
can be replaced (or its delivery path compromised) after upload. The next
step builds the AppImage with the Tauri signing private key and a
contents:write GITHUB_TOKEN in scope, so a substituted linuxdeploy that
ran during packaging could exfiltrate signing material or tamper with
published release artifacts.
Pin the immutable SHA-256 of the asset and verify it with sha256sum -c
before chmod +x, so a mismatch fails the job closed before the binary is
ever executable. Extend the existing in-workflow guard to require both the
pinned digest and the verification step, so a future edit cannot silently
drop the check.
* Scope linuxdeploy guard to real step content, not its own text
The self-check searched every workflow line, so the digest assertion was
satisfied by the guard's own expectedLinuxdeployDigest line and the
verification assertion by a comment. Deleting the LINUXDEPLOY_SHA256 env
pin or the actual sha256sum -c command would still have passed.
Match the digest against the LINUXDEPLOY_SHA256 env line specifically and
require sha256sum -c on a non-comment line, so dropping either the pin or
the verification now fails the guard.
* Scope linuxdeploy guard to the Pin step block and check ordering
The previous predicate still scanned the whole workflow, so the literal
sha256sum -c in the guard's own code satisfied the verification check; a
deleted or post-chmod verification command would still pass.
Extract the 'Pin linuxdeploy for AppImage' step block and assert within it:
the LINUXDEPLOY_SHA256 env pins the expected digest, a non-comment line
runs sha256sum -c, and that verification precedes chmod +x.
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