fix(core): read database errors handed to from_api as internal, not offline

from_api took every error that was not a ProtonError for a transport
failure. Pin, unpin, the searches and node loads hand it pdfs_core
errors from the cache and the database, so a failure there said
"You're offline" (B266, the rest of B205). The source chain now
decides, and only an error with neither type reads as offline.

crates/pdfs-core/src/error.rs

@@ -160,13 +160,14 @@ impl CoreError {
     /// telling the user their connection is down beats telling them the
     /// server refused. The SDK's other failures say what went wrong instead
     /// (see [`proton_kind`]).
+    ///
+    /// Callers also hand it this crate's [`Error`] from the cache and the
+    /// database, which is not a transport error at all. Taking those for
+    /// "offline" told the user their connection was down when a pin failed on
+    /// the database (`docs/BUGS.md` B266), so the source chain is searched for
+    /// either type before falling back.
     pub fn from_api(e: &(dyn std::error::Error + 'static), what: &str) -> Self {
-        let kind = match e.downcast_ref::<proton_sdk::ProtonError>() {
-            Some(proton) => proton_kind(proton),
-            // Not the SDK's at all: a timeout around the call, or the socket.
-            None => ErrorKind::Offline,
-        };
-        Self::new(kind, format!("{what}: {e}"))
+        Self::new(api_kind_of(e), format!("{what}: {e}"))
     }
 
     /// Prefix the message while keeping the classification.
@@ -208,19 +209,40 @@ impl From<serde_json::Error> for CoreError {
 
 impl From<Error> for CoreError {
     fn from(e: Error) -> Self {
-        let kind = match &e {
-            Error::NotLoggedIn
-            | Error::ReloginRequired
-            | Error::Locked
-            | Error::WrongMailboxPassword
-            | Error::HumanVerificationRequired(_) => ErrorKind::Denied,
-            Error::Proton(proton) => proton_kind(proton),
-            _ => ErrorKind::Internal,
-        };
-        Self::new(kind, e.to_string())
+        Self::new(core_kind(&e), e.to_string())
     }
 }
 
+/// What this crate's [`Error`] means to a front-end.
+fn core_kind(e: &Error) -> ErrorKind {
+    match e {
+        Error::NotLoggedIn
+        | Error::ReloginRequired
+        | Error::Locked
+        | Error::WrongMailboxPassword
+        | Error::HumanVerificationRequired(_) => ErrorKind::Denied,
+        Error::Proton(proton) => proton_kind(proton),
+        _ => ErrorKind::Internal,
+    }
+}
+
+/// The kind for [`CoreError::from_api`]: the first SDK or crate error in `e`'s
+/// source chain decides it.
+fn api_kind_of(e: &(dyn std::error::Error + 'static)) -> ErrorKind {
+    let mut cause = Some(e);
+    while let Some(err) = cause {
+        if let Some(proton) = err.downcast_ref::<proton_sdk::ProtonError>() {
+            return proton_kind(proton);
+        }
+        if let Some(core) = err.downcast_ref::<Error>() {
+            return core_kind(core);
+        }
+        cause = err.source();
+    }
+    // Not the SDK's at all: a timeout around the call, or the socket.
+    ErrorKind::Offline
+}
+
 /// What a failed SDK call means to a front-end.
 ///
 /// Only a transport failure is the connection. The rest happened on this
@@ -414,6 +436,20 @@ mod tests {
         assert_ne!(e.kind, ErrorKind::Offline);
     }
 
+    /// A pin or a search that fails on the database is not the connection, so
+    /// it must not say "You're offline" (`docs/BUGS.md` B266). An SDK error
+    /// wrapped in this crate's type classifies as the SDK error does.
+    #[test]
+    fn a_database_error_handed_to_from_api_is_not_offline() {
+        let db = Error::Other("database is locked".into());
+        assert_eq!(CoreError::from_api(&db, "pin").kind, ErrorKind::Internal);
+        let wrapped = Error::Proton(api(C::DoesNotExist));
+        assert_eq!(
+            CoreError::from_api(&wrapped, "load node").kind,
+            ErrorKind::NotFound
+        );
+    }
+
     /// `Error` is the plumbing type; converting it must classify as sharply as
     /// the direct path, or the two disagree about the same failure.
     #[test]

docs/BUGS.md

@@ -75,7 +75,6 @@ original wording.
 | [B269](#b269--a-restore-that-skipped-every-folder-reports-success) | A restore that skipped every folder reports success | Not fixed |
 | [B268](#b268--pdfs-diagnose-says-no-problems-found-while-sync-is-stuck) | `pdfs diagnose` says "No problems found" while sync is stuck | Not fixed |
 | [B267](#b267--a-key-failure-at-a-start-from-a-warm-cache-shows-as-offline-for-good) | A key failure at a start from a warm cache shows as offline for good | Not fixed |
-| [B266](#b266--pin-unpin-search-and-node-loads-report-a-database-error-as-offline) | Pin, unpin, search and node loads report a database error as "offline" | Not fixed |
 | [B265](#b265--address-keys-whose-token-is-for-an-inactive-account-key-never-open) | Address keys whose token is for an inactive account key never open | Needs an SDK change; not reproduced |
 | [B264](#b264--a-mount-that-fails-after-starting-its-workers-leaves-them-running) | A mount that fails after starting its workers leaves them running | Not fixed |
 | [B263](#b263--a-mount-that-can-never-succeed-retries-every-5-s-and-tells-only-the-journal) | A mount that can never succeed retries every 5 s and tells only the journal | Not fixed |
@@ -116,6 +115,7 @@ a live account since.
 
 | Entry | Title |
 |---|---|
+| [B266](#b266--pin-unpin-search-and-node-loads-report-a-database-error-as-offline) | Pin, unpin, search and node loads report a database error as "offline" |
 | [B256](#b256--pdfs-copy-right-after-a-save-copies-the-old-version) | `pdfs copy` right after a save copies the old version |
 | [B255](#b255--a-synced-folder-whose-files-are-all-gone-here-is-stuck-for-good) | A synced folder whose files are all gone here is stuck for good |
 | [B254](#b254--an-edit-in-the-same-second-as-a-new-upload-never-arrives) | An edit in the same second as a new upload never arrives |
@@ -523,7 +523,7 @@ report the others as their own state through `Status`.
 
 ### B266 — Pin, unpin, search and node loads report a database error as "offline"
 
-**Status:** Open
+**Status:** Fixed, not verified live
 **Found:** 2026-10-31, code audit after issue #38. B205 fixed the photo upload path only.
 **Where:** `CoreError::from_api` in `crates/pdfs-core/src/error.rs`; its callers in
 `crates/pdfs-fuse/src/lib.rs` (`pin`, `unpin`, the searches, `load node`)
@@ -536,8 +536,11 @@ it was written for SDK calls, where that means a transport error. These callers
 `pdfs_core::Error` values from the cache and the database. A `ProtonError` wrapped in
 `pdfs_core::Error::Proton` also misses the downcast, since the source chain is not walked.
 
-**Fix.** Not done. Use `CoreError::internal` at the database callers, and walk the source
-chain in `from_api` before falling back.
+**Fix.** `from_api` walks the source chain. The first `ProtonError` or `pdfs_core::Error` in it
+decides the kind, the same way `From<Error>` does, and only an error with neither, a transport
+error, reads as offline. That covers every caller at once, the database ones included.
+
+**Test:** `a_database_error_handed_to_from_api_is_not_offline` in `pdfs-core`.
 
 ---