feat: HTTP server for exporting Arborix bundles

Introduces a read-only HTTP server (WAI/Warp) backed by the content
store, exposing three bundle-export endpoints:

- GET /bundle/name/:name   — export by stored term name
- GET /bundle/hash/:hash   — export by full Merkle hash
- GET /terms               — plain-text listing (debug)

Also adds `tricu server` (aka `--serve`) CLI mode, move `resolveExportTarget` /
 `namesForHash` / `looksLikeHash` out of `Main.hs` into `ContentStore.hs`,
and cleans up unused exports and imports across `FileEval.hs` and `Wire.hs`.

src/Server.hs

@@ -0,0 +1,176 @@
+module Server
+  ( runServer
+  ) where
+
+import ContentStore (initContentStore, nameToTerm, hashToTerm, listStoredTerms,
+                     parseNameList, StoredTerm(..), termHash)
+import Database.SQLite.Simple (close)
+import Wire (exportNamedBundle)
+
+import Network.HTTP.Types (Header, Status, status200, status400, status404, status405, hContentType)
+import Network.Wai
+import Network.Wai.Handler.Warp (defaultSettings, runSettings, setHost, setPort)
+
+import Data.String (fromString)
+import Data.Text (Text)
+import Data.Text.Encoding (encodeUtf8)
+import Data.Char (isHexDigit)
+import Data.ByteString.Lazy (fromStrict)
+
+import qualified Data.Text as T
+
+-- | Start an HTTP server that serves Arborix bundles from the
+--   local content store.
+--
+-- This is a read-only export surface.  Clients fetch bundle bytes
+-- and independently inspect / verify / run them.  The server does
+-- not execute bundles.
+--
+-- Bind host defaults to @127.0.0.1@.
+--
+-- Endpoints
+-- ---------
+--   GET /health                   — 200 "ok"
+--   GET /bundle/name/:name        — export by stored term name
+--   GET /bundle/hash/:hash        — export by full Merkle hash
+--   GET /terms                    — plain-text listing (debug)
+--
+runServer :: String -> Int -> IO ()
+runServer hostStr port =
+  runSettings settings app
+  where
+    settings = setPort port $ setHost (fromString hostStr) defaultSettings
+
+-- | WAI application backed by the content store.
+--   Uses the same database path as @eval@ mode (env var
+--   @TRICU_DB_PATH@ or the default location).
+app :: Application
+app request respond = case (requestMethod request, pathInfo request) of
+  ("GET", ["health"]) ->
+    respond $ healthResponse
+
+  ("GET", ["bundle", "name", nameText]) -> do
+    body <- nameHandler nameText
+    respond body
+
+  ("GET", ["bundle", "hash", hashText]) -> do
+    body <- hashHandler hashText
+    respond body
+
+  ("GET", ["terms"]) -> do
+    body <- termsResponse
+    respond body
+
+  ("POST", _) ->
+    respond $ responseLBS status405 [] "Method not allowed"
+
+  ("PUT", _) ->
+    respond $ responseLBS status405 [] "Method not allowed"
+
+  ("DELETE", _) ->
+    respond $ responseLBS status405 [] "Method not allowed"
+
+  _ ->
+    respond $ responseLBS status404 [] "not found"
+
+healthResponse :: Response
+healthResponse = responseLBS status200 [] "ok"
+
+-- | GET /bundle/name/:name
+--   Resolve a stored term name, export it as an Arborix bundle,
+--   and return the raw bundle bytes.
+--
+--   Sets @Content-Type@ and @X-Arborix-Root-Hash@ headers.
+--   Returns 404 when the name does not resolve to any stored term.
+nameHandler :: Text -> IO Response
+nameHandler nameText = do
+  conn <- initContentStore
+  stored <- nameToTerm conn nameText
+  case stored of
+    Nothing -> do
+      close conn
+      return $ textResponse status404 ("not found: " <> nameText)
+    Just term' -> do
+      let th = termHash term'
+          namedHashes = [(firstOrRoot (termNames term'), th)]
+      bundleData <- exportNamedBundle conn namedHashes
+      let cd = T.pack $ "attachment; filename=" ++ safeFileName (T.unpack nameText) ++ ".bundle"
+      close conn
+      return $ responseLBS status200 (bundleHeaders th cd) (fromStrict bundleData)
+
+-- | GET /bundle/hash/:hash
+--   Resolve a full Merkle hash and export the root as an Arborix
+--   bundle.
+--
+--   - Malformed hash (non-hex or < 16 chars): 400
+--   - Well-formed but absent: 404
+--   - Present: 200 with bundle bytes
+hashHandler :: Text -> IO Response
+hashHandler hashText =
+  let raw = T.pack (dropWhile (== '#') (T.unpack hashText))
+  in if not (T.all isHexDigit raw) || T.length raw < 16
+        then return $ responseLBS status400 [] "400 Bad Request: invalid hash"
+        else do
+          conn <- initContentStore
+          stored <- hashToTerm conn raw
+          case stored of
+            Nothing -> do
+              close conn
+              return $ textResponse status404 ("not found: " <> hashText)
+            Just term' -> do
+              let th = termHash term'
+                  namedHashes' = [(firstOrRoot (termNames term'), th)]
+              bundleData <- exportNamedBundle conn namedHashes'
+              close conn
+              return $ responseLBS status200
+                (bundleHeaders th "attachment; filename=hash.bundle")
+                (fromStrict bundleData)
+
+-- | GET /terms
+--   Plain-text listing of all stored terms (debugging only).
+termsResponse :: IO Response
+termsResponse = do
+  conn <- initContentStore
+  terms <- listStoredTerms conn
+  close conn
+  let lines' = [ names <> "  " <> hash <> "  " <> T.pack (show created)
+               | term <- terms
+               , let names = termNames term
+               , let hash = termHash term
+               , let created = termCreatedAt term ]
+  return $ responseLBS status200
+    [ (hContentType, encodeUtf8 "text/plain; charset=utf-8")
+    ]
+    (fromStrict $ encodeUtf8 $ T.unlines lines')
+
+textResponse :: Status -> Text -> Response
+textResponse status body =
+  responseLBS status
+    [ (hContentType, encodeUtf8 "text/plain; charset=utf-8") ]
+    (fromStrict $ encodeUtf8 body)
+
+bundleHeaders :: Text -> Text -> [Header]
+bundleHeaders root cd =
+  [ (hContentType, encodeUtf8 "application/vnd.arborix.bundle")
+  , ("X-Arborix-Root-Hash", encodeUtf8 root)
+  , ("Content-Disposition", encodeUtf8 cd)
+  ]
+
+-- | Pick the first stored name, falling back to "root" when names are empty.
+firstOrRoot :: Text -> Text
+firstOrRoot names =
+  case parseNameList names of
+    [] -> "root"
+    (x:_) -> x
+
+-- | Sanitise a string to a safe filename prefix.
+safeFileName :: String -> String
+safeFileName = map go
+  where
+    go c
+      | c >= 'a' && c <= 'z' = c
+      | c >= 'A' && c <= 'Z' = c
+      | c >= '0' && c <= '9' = c
+      | c == '-' = c
+      | c == '_' = c
+      | otherwise = '_'