feat(mcp): add policy_cbor_path arg to wallet_plutus_mint_unsigned

Mirrors the reference_script_path workaround already on wallet_send.
Lets the caller hand aldabra a path to a hex-CBOR file inside the
container instead of pasting the hex inline as a JSON-RPC arg, which
lets us bypass the 2026-05-07 MCP large-string transport bug (>~ 4500
char hex strings get a 1-byte truncation between Claude Code and
aldabra's stdio reader, surfacing as 'odd length' decode errors and
blocking debug-build minting policies).

policy_cbor_hex becomes Option<String>; new policy_cbor_path:
Option<String> sits next to it. New resolver helper
resolve_policy_cbor_bytes mirrors resolve_ref_script_bytes — at most
one of the two may be set, exactly one must be set. Whitespace is
stripped from file contents so the file may have trailing newlines.

Unblocks Track #33 / preprod_test3: debug-build validators that
overshoot the transport ceiling can now be minted via path arg.

crates/aldabra-mcp/src/tools.rs

@@ -103,6 +103,48 @@ fn resolve_ref_script_bytes(
     }
 }
 
+/// Resolve the Plutus minting-policy CBOR from EITHER an inline
+/// hex argument OR a file path inside the container. Caller passes
+/// both raw options; this fn enforces the "exactly one" rule and
+/// reads the file when path is set.
+///
+/// Mirrors [`resolve_ref_script_bytes`] — same workaround for the
+/// 2026-05-07 MCP transport bug where hex strings >~ 4500 chars
+/// get a 1-byte truncation between Claude Code and aldabra's stdio
+/// reader, surfacing as "odd length" hex decode errors and blocking
+/// debug-build minting policies. Reading from a file inside the
+/// container bypasses the JSON-RPC arg path entirely.
+fn resolve_policy_cbor_bytes(
+    cbor_hex: Option<&str>,
+    path: Option<&str>,
+) -> Result<Vec<u8>, String> {
+    match (cbor_hex, path) {
+        (Some(_), Some(_)) => Err(
+            "set at most one of policy_cbor_hex / policy_cbor_path".into(),
+        ),
+        (Some(s), None) => {
+            let cleaned: String = s.chars().filter(|c| !c.is_whitespace()).collect();
+            hex_decode(&cleaned).map_err(|e| format!("decode policy_cbor_hex: {e}"))
+        }
+        (None, Some(p)) => {
+            let raw = std::fs::read_to_string(p)
+                .map_err(|e| format!("read policy_cbor_path '{p}': {e}"))?;
+            let cleaned: String = raw.chars().filter(|c| !c.is_whitespace()).collect();
+            if cleaned.is_empty() {
+                return Err(format!(
+                    "policy_cbor_path '{p}' contained no hex characters"
+                ));
+            }
+            hex_decode(&cleaned).map_err(|e| {
+                format!("decode policy_cbor_path '{p}' contents: {e}")
+            })
+        }
+        (None, None) => {
+            Err("must set exactly one of policy_cbor_hex / policy_cbor_path".into())
+        }
+    }
+}
+
 /// Parse a user-supplied script-kind string ("PlutusV1" / "PlutusV2"
 /// / "PlutusV3" / "Native") into the pallas `ScriptKind` enum used
 /// by the reference-script attachment helper. Case-insensitive,
@@ -398,7 +440,22 @@ pub struct PolicyCreateArgs {
 pub struct PlutusMintUnsignedArgs {
     /// Plutus minting policy script CBOR (hex). 28-byte blake2b
     /// hash with the version tag becomes the policy_id.
-    pub policy_cbor_hex: String,
+    /// At most one of `policy_cbor_hex` or `policy_cbor_path` may
+    /// be set; exactly one must be set.
+    #[serde(default)]
+    pub policy_cbor_hex: Option<String>,
+    /// Path INSIDE THE ALDABRA CONTAINER to a file containing
+    /// hex-encoded Plutus policy CBOR. Use INSTEAD of
+    /// `policy_cbor_hex` for scripts >~ 4500 chars to bypass the
+    /// MCP large-string transport bug (caught 2026-05-07: hex strings
+    /// > ~4500 chars get a 1-byte truncation + structural rearrangement
+    /// somewhere between Claude Code and aldabra's stdio reader,
+    /// surfacing as "odd length" hex decode errors). File contents
+    /// may include leading/trailing whitespace; only hex chars are
+    /// decoded. At most one of `policy_cbor_hex` or `policy_cbor_path`
+    /// may be set; exactly one must be set.
+    #[serde(default)]
+    pub policy_cbor_path: Option<String>,
     /// Plutus version: "v1", "v2", or "v3".
     pub policy_version: String,
     /// PlutusData CBOR redeemer (hex) for the mint redeemer entry.
@@ -1612,12 +1669,13 @@ impl WalletService {
 
     #[tool(
         name = "wallet_plutus_mint_unsigned",
-        description = "Build (no sign) a Plutus-policy mint with custom output. Distinct from wallet_mint (native script only). Args: policy_cbor_hex + policy_version (v1/v2/v3) + redeemer_cbor_hex + ex_units (mem+steps), mint_assets (array of {asset_name_hex, quantity}), dest_address + dest_lovelace + dest_extra_assets + dest_inline_datum_cbor_hex (req for script addrs), required_input_refs (array of 'txhash#index' UTxOs that MUST be spent — e.g. gstOutRef for parameterized policies). Returns JSON {cbor_hex, summary}. Pass through wallet_sign_partial → wallet_submit_signed_tx. Designed for Agora-style DAO bringup: governor bootstrap, stake bootstrap, proposal create."
+        description = "Build (no sign) a Plutus-policy mint with custom output. Distinct from wallet_mint (native script only). Args: policy_cbor_hex OR policy_cbor_path (use path for >~4500-char scripts to bypass the MCP large-string transport bug) + policy_version (v1/v2/v3) + redeemer_cbor_hex + ex_units (mem+steps), mint_assets (array of {asset_name_hex, quantity}), dest_address + dest_lovelace + dest_extra_assets + dest_inline_datum_cbor_hex (req for script addrs), required_input_refs (array of 'txhash#index' UTxOs that MUST be spent — e.g. gstOutRef for parameterized policies). Returns JSON {cbor_hex, summary}. Pass through wallet_sign_partial → wallet_submit_signed_tx. Designed for Agora-style DAO bringup: governor bootstrap, stake bootstrap, proposal create."
     )]
     async fn wallet_plutus_mint_unsigned(
         &self,
         #[tool(aggr)] PlutusMintUnsignedArgs {
             policy_cbor_hex,
+            policy_cbor_path,
             policy_version,
             redeemer_cbor_hex,
             mint_assets,
@@ -1639,8 +1697,10 @@ impl WalletService {
             ));
         }
 
-        let policy_cbor =
-            hex_decode(&policy_cbor_hex).map_err(|e| format!("decode policy_cbor: {e}"))?;
+        let policy_cbor = resolve_policy_cbor_bytes(
+            policy_cbor_hex.as_deref(),
+            policy_cbor_path.as_deref(),
+        )?;
         let redeemer_cbor =
             hex_decode(&redeemer_cbor_hex).map_err(|e| format!("decode redeemer: {e}"))?;
         let policy_ver = match policy_version.trim().to_ascii_lowercase().as_str() {