v0.79.0: escrow upload carries restic_pw_sha256 (SLICE 3 auto-confirm, agent third)

HashResticPassword = sha256 hex over the trimmed password (pinned
cross-repo vector). escrowUploadRequest gains restic_pw_sha256,omitempty
— set only when a staged password was sealed into the blob. Contract test
updated; hub mirrors next.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

internal/escrow/identity.go

@@ -2,7 +2,9 @@ package escrow
 
 import (
 	"context"
+	"crypto/sha256"
 	"encoding/base64"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -53,6 +55,17 @@ func WipeStagedResticPassword() error {
 	return nil
 }
 
+// HashResticPassword is the CANONICAL hasher for the offsite restic repo password (SLICE 3 hub-verified
+// escrow auto-confirm): sha256 hex of the TRIMMED password string — exactly the value AttachResticPassword
+// seals into the blob and the value the controller uses (both sides TrimSpace their file reads, so the
+// trimmed string is the drift-free convention; pinned by the SAME test vector in felhom-agent and
+// felhom-controller). The hash of a 256-bit random secret is non-reversible and non-brute-forceable —
+// safe to store on the hub and serve in report ACKs; the PASSWORD itself is never logged or served.
+func HashResticPassword(pw string) string {
+	sum := sha256.Sum256([]byte(strings.TrimSpace(pw)))
+	return hex.EncodeToString(sum[:])
+}
+
 // AttachResticPassword injects the offsite restic repo password from the staged 0600 file into the bundle
 // when it exists (fork-4 escrow-create auto-inject). Returns whether it attached. The VALUE is validated
 // (non-empty) but NEVER logged by callers — log the field NAME only (mirrors AttachWGKey). A missing file