fix(approval): undelivered or unanswered CLI approval prompts are not user denials

When the CLI approval callback raises, when no callback is registered on the
thread while prompt_toolkit owns the terminal, or when the input() read is
interrupted, prompt_dangerous_approval returned "deny" and the command gate
rendered "BLOCKED: User denied this command" — attributing a refusal to a
user who was never asked (#22992). #112308 fixed the gateway half of the
class (withdrawn prompts -> outcome "cancelled" with a cause); this closes
the CLI residual on the same shape.

- tools/approval_prompt.py: those three paths return an Unanswered("cancelled")
  sentinel carrying the cause; MCP elicitation consent maps it to "cancel".
- tools/approval.py: the CLI gate renders "BLOCKED: <noun> was not approved: the
  approval prompt could not be delivered or was not answered (<cause>)" with
  outcome "cancelled" — still fail-closed, "Silence is not consent".
- tools/file_tools_write_guards.py: the protected-instruction write gate
  reports the undelivered prompt instead of "was denied by the user".
- Shared metrics: "cancelled" is a counted approval outcome (contract + v2
  schema) instead of falling into "unknown".
- Docs: hook `choice="cancelled"` now covers the CLI causes.

Fixes #22992

hermes_cli/observability/schemas/hermes.shared_metrics.v2.schema.json

@@ -493,6 +493,7 @@
             "approval_outcome": {
               "enum": [
                 "approved",
+                "cancelled",
                 "denied",
                 "not_required",
                 "timed_out",
@@ -578,6 +579,7 @@
             "outcome": {
               "enum": [
                 "approved",
+                "cancelled",
                 "denied",
                 "timed_out",
                 "unknown"

hermes_cli/observability/shared_metrics_contract.py

@@ -61,7 +61,7 @@ TOOL_CATEGORIES = frozenset({
     "skill", "terminal", "unknown", "web",
 })
 TOOL_OUTCOMES = frozenset({"blocked", "cancelled", "failed", "success", "timed_out", "unknown"})
-TOOL_APPROVAL_OUTCOMES = frozenset({"approved", "denied", "not_required", "timed_out", "unknown"})
+TOOL_APPROVAL_OUTCOMES = frozenset({"approved", "cancelled", "denied", "not_required", "timed_out", "unknown"})
 TOOL_APPROVAL_ATTRIBUTIONS = frozenset({"tool_call", "unattributed"})
 TOOL_LATENCY_BUCKETS = frozenset({
     "100ms_to_250ms", "10s_to_30s", "1s_to_2s", "250ms_to_500ms", "2s_to_5s", "500ms_to_1s",
@@ -548,6 +548,7 @@ _APPROVAL_CHOICES = {
     ),
     **dict.fromkeys(("deny", "denied", "smart_deny"), "denied"),
     **dict.fromkeys(("timed_out", "timeout"), "timed_out"),
+    "cancelled": "cancelled",  # prompt withdrawn / undeliverable / unanswered — not a user decision
 }