Trust the OS certificate store for engine HTTPS requests (#757) (#759)

The engine verified TLS against the Mozilla roots bundled through
webpki-roots only, so behind a TLS-inspecting proxy (Aikido, Zscaler,
Netskope) whose root lives in the OS trust store, `impeccable update`
and `install` failed with `invalid peer certificate: UnknownIssuer`
while curl and npm on the same machine succeeded.

crates/context/src/http.rs builds one rustls ClientConfig per process:
the OS trust store (rustls-native-certs: Keychain, Windows store, the
OpenSSL paths on Linux) merged with the bundled roots. A union, not a
replacement, so a container without ca-certificates or a store that
fails to load still verifies exactly as before. SSL_CERT_FILE and
SSL_CERT_DIR replace the OS store the way they do for OpenSSL and curl.
Every HTTPS call site (bundle and signature downloads, /api/version,
/api/commands, the roll API, image generation) builds its agent from
this module; the plain-HTTP live-server calls on localhost are
untouched.

Verified against a local HTTPS server signed by a throwaway CA: trusted
through SSL_CERT_FILE the update check reaches it; without it the same
server is rejected as UnknownIssuer; with SSL_CERT_FILE pointing at that
CA or at a missing file, impeccable.style still verifies through the
bundled roots. cargo test --workspace and the oracle corpus (832) pass.

Written with AI assistance (Claude Code).

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

Cargo.lock

@@ -111,6 +111,22 @@ version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3d7b894f5411737b7867f4827955924d7c254fc9f4d91a6aad6b097804b1018b"
 
+[[package]]
+name = "core-foundation"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b2a6cd9ae233e7f62ba4e9353e81a88df7fc8a5987b8d445b4d90c879bd156f6"
+dependencies = [
+ "core-foundation-sys",
+ "libc",
+]
+
+[[package]]
+name = "core-foundation-sys"
+version = "0.8.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "773648b94d0e5d620f64f280777445740e61fe701025087ec8b57f45c791888b"
+
 [[package]]
 name = "cpufeatures"
 version = "0.2.17"
@@ -590,12 +606,14 @@ dependencies = [
  "impeccable-core",
  "once_cell",
  "regex",
+ "rustls-native-certs",
  "serde",
  "serde_json",
  "sha2",
  "tiny_http",
  "unicode-normalization",
  "ureq",
+ "webpki-roots 1.0.9",
 ]
 
 [[package]]
@@ -830,6 +848,12 @@ version = "1.21.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
 
+[[package]]
+name = "openssl-probe"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7c87def4c32ab89d880effc9e097653c8da5d6ef28e6b539d313baaacfbafcbe"
+
 [[package]]
 name = "parking_lot"
 version = "0.12.5"
@@ -1063,7 +1087,7 @@ dependencies = [
  "getrandom 0.2.17",
  "libc",
  "untrusted",
- "windows-sys",
+ "windows-sys 0.52.0",
 ]
 
 [[package]]
@@ -1096,6 +1120,18 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "rustls-native-certs"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dab5152771c58876a2146916e53e35057e1a4dfa2b9df0f0305b07f611fdea4d"
+dependencies = [
+ "openssl-probe",
+ "rustls-pki-types",
+ "schannel",
+ "security-framework",
+]
+
 [[package]]
 name = "rustls-pki-types"
 version = "1.15.1"
@@ -1122,6 +1158,15 @@ version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf54715a573b99ac80df0bc206da022bcd442c974952c7b9720069370852e21f"
 
+[[package]]
+name = "schannel"
+version = "0.1.29"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "91c1b7e4904c873ef0710c1f407dde2e6287de2bebc1bbbf7d430bb7cbffd939"
+dependencies = [
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -1142,6 +1187,29 @@ dependencies = [
  "tendril",
 ]
 
+[[package]]
+name = "security-framework"
+version = "3.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7f4bc775c73d9a02cde8bf7b2ec4c9d12743edf609006c7facc23998404cd1d"
+dependencies = [
+ "bitflags",
+ "core-foundation",
+ "core-foundation-sys",
+ "libc",
+ "security-framework-sys",
+]
+
+[[package]]
+name = "security-framework-sys"
+version = "2.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ce2691df843ecc5d231c0b14ece2acc3efb62c0a398c7e1d875f3983ce020e3"
+dependencies = [
+ "core-foundation-sys",
+ "libc",
+]
+
 [[package]]
 name = "selectors"
 version = "0.38.0"
@@ -1603,6 +1671,15 @@ dependencies = [
  "windows-targets",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
 [[package]]
 name = "windows-targets"
 version = "0.52.6"