refactor(tarball): expose one cache identity, not two (#15038)

Nothing outside the crate builds a cache key for a projection other than
the ordinary package one, so `ArchiveStoreProjection::mem_cache_key` goes
back to being internal and `package_mem_cache_key` carries the contract.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

pnpm/crates/tarball/src/download.rs

@@ -61,21 +61,10 @@ impl<'a> ArchiveStoreProjection<'a> {
         }
     }
 
-    /// Identity of the archive a shared [`crate::MemCache`] slot holds.
-    ///
-    /// The expected hash is part of it: a slot's bytes were verified against
-    /// one integrity, and a request pinning a different one must not be
-    /// served them. An archive whose hash the fetch discovers is published
-    /// under the computed hash, which is the one its resolution then records.
-    /// Projections that can produce a different file set carry their own
-    /// discriminator; synthesized manifests are content-addressed so equal
-    /// projections still share work.
-    ///
-    /// The parts are tab-separated, and neither a URL, an integrity, nor a
-    /// projection tag can contain a tab, so two distinct identities cannot
-    /// spell the same key.
-    #[must_use]
-    pub fn mem_cache_key(
+    /// Identity of the archive a shared [`crate::MemCache`] slot holds. See
+    /// [`package_mem_cache_key`], the shape every caller outside this crate
+    /// uses.
+    pub(crate) fn mem_cache_key(
         self,
         package_url: &str,
         integrity: Option<&Integrity>,
@@ -117,7 +106,20 @@ impl<'a> ArchiveStoreProjection<'a> {
 
 /// Cache identity of an ordinary package archive, the projection every
 /// resolve-time publisher, speculative prefetch and install-time lookup
-/// has to agree on. See [`ArchiveStoreProjection::mem_cache_key`].
+/// has to agree on.
+///
+/// The expected hash is part of it: a slot's bytes were verified against
+/// one integrity, and a request pinning a different one must not be served
+/// them. An archive whose hash the fetch discovers is published under the
+/// computed hash, which is the one its resolution then records. The network
+/// policy is part of it too, since a revision-addressed fetch and a direct
+/// one are different requests for the same URL. Projections that can produce
+/// a different file set carry their own discriminator; synthesized manifests
+/// are content-addressed so equal projections still share work.
+///
+/// The parts are tab-separated, and neither a URL, an integrity, nor a
+/// projection tag can contain a tab, so two distinct identities cannot spell
+/// the same key.
 #[must_use]
 pub fn package_mem_cache_key(
     package_url: &str,

pnpm/crates/tarball/src/lib.rs

@@ -206,7 +206,8 @@ impl<'a> IngestTarballToStore<'a> {
     ///
     /// # Caller invariant: stable filter per archive
     ///
-    /// The cache is keyed on [`ArchiveStoreProjection::mem_cache_key`]. Within
+    /// The cache is keyed on the archive's identity, which
+    /// [`package_mem_cache_key`] spells for an ordinary package. Within
     /// one key, a second caller fetching the same archive with a different
     /// [`ignore_file_pattern`] silently receives the map the first caller's
     /// filter produced. Every fetch of an archive must use the same filter.