feat(migration): sync plugin for the legacy dfx 0.32.0 assetstorage canister

[lwshang]

⚠️ This branch is never merged into main

The migration branch is a permanently separate line of work. Do not merge it.

Instead, we will git-tag commits on this branch and cut special GitHub releases that host the built sync-plugin wasm module. icp-cli projects (recipes, templates) reference that hosted wasm directly.

The driving use case: a companion assets recipe that swaps the sync mechanism from the old type: assets to type: plugin while keeping the canister wasm unchanged (the legacy dfx 0.32.0 assetstorage canister). This minimizes the upgrade effort for existing assets-recipe users when we drop type: assets sync in the upcoming icp-cli release.

What this branch does

Retargets sync-core / sync-plugin from this repo's V2 certified-assets canister to the legacy assetstorage canister shipped with dfx 0.32.0 (ic-certified-assets, which reports api_version == 2). Per-asset metadata is read from .ic-assets.json5 (full ic-asset parity) instead of the _headers / _redirects files used on main.

The legacy canister's wire protocol is nearly identical to this repo's V2 canister; the differences are narrow and handled here:

Concern	main (new)	legacy (0.32.0)
Redirect rules	get_redirect_rules / SetRedirectRules	absent (removed)
CreateAssetArguments	—	adds enable_aliasing
SetAssetPropertiesArguments	—	adds is_aliased
AssetProperties	—	adds is_aliased
Per-asset config	_headers + _redirects	.ic-assets.json5
HTML routing	synthesised redirect rules	native enable_aliasing

sync-core

• new config.rs — .ic-assets.json5 / .ic-assets.json parser ported from ic-asset: nested config inheritance, glob match, ignore, headers, cache.max_age, enable_aliasing, allow_raw_access, encodings, security_policy.
• new security_policy.rs — standard / hardened / disabled CSP presets.
• scan.rs rewritten as gather_asset_descriptors (walkdir + config-driven ignore; .well-known kept; config files excluded).
• canister.rs — add enable_aliasing / is_aliased; drop RedirectRule / RulePattern / SetRedirectRules / get_redirect_rules.
• sync.rs — drive CreateAsset / SetAssetProperties from AssetConfig; drop redirect & html-handling; keep chunk packing + commit staging.
• delete redirects.rs, headers.rs, html_handling.rs, glob.rs.
• idempotency fix: the legacy canister injects a Set-Cookie: ic_env=... header into every HTML asset (driven by icp-cli's env-var step) and returns it from get_asset_properties. update_properties now ignores that canister-managed cookie so repeat syncs report "up to date" instead of clobbering it every run.

e2e

• build.rs fetches the real assetstorage.wasm.gz from the dfx 0.32.0 release (sha256-pinned to the GH release digest, installed gzipped — no decompression) instead of building this repo's canister.
• fixtures/tests converted to .ic-assets.json5; redirect / header / multi-dir cases removed; new config.rs end-to-end test (headers, max_age, aliasing, security_policy CSP, config-file-not-uploaded).

Test plan

• cargo test -p sync-core — 75 unit tests pass.
• cargo build -p sync-plugin --target wasm32-wasip2 --release — links under WASI.
• cargo test -p e2e — deploys the real 0.32.0 assetstorage.wasm and exercises the plugin via icp deploy; config test + all sync tests (incl. idempotent no_op_sync) pass.

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