feat: general gated run primitive + chat-assent approval (Layer 0)

Implements the first slice of plans/2026-07-10-general-gated-execution.md:
Nomos gets one general execution tool instead of only a fixed action enum,
gated by an automatic risk classifier, and approval can be granted by the
operator just replying in chat instead of clicking a button.

- internal/policy/command.go: ClassifyCommand(cmd, declaredRisk) — rule-based
  read-only allowlist + destructive denylist, default-escalate to
  config_mutation for anything else. Classification can only ESCALATE the
  caller's declared risk, never de-escalate it (destructive always wins even
  if declared read_only). Compound commands (&&, ;, |, $()) never qualify for
  the read-only fast path. Full test corpus.
- internal/mcp/server.go: new `run` MCP tool — target (host:/lxc:), command,
  purpose, optional declared_risk. Read-only commands execute immediately;
  everything else queues an approval exactly like pct_create today, executed
  via httpapi's existing executeApprovedAction. Also fixes a real latent bug:
  pct_exec resolved an LXC's host attribute without the "host:" prefix, so it
  could never find the Proxmox host — new resolveExecTarget/resolveRunTarget
  helpers (mcp + httpapi) fix this for both the new `run` action and existing
  actions that route through the same execution path.
- internal/httpapi/phase3.go: "run" case in executeApprovedAction; fixes two
  bugs found while wiring this up — (1) DecideApproval hardcoded risk_class to
  'config_mutation' on every approve, silently corrupting the audit ledger for
  every other risk class; (2) denying/revoking an approval never updated the
  linked execution's status, so it stayed 'pending_approval' forever instead
  of reflecting the decision.
- cmd/nomos/assent.go: deterministic (not LLM-judged) chat-assent detection.
  Scoped to the immediately-preceding assistant turn's pending approvals only
  — an old "yes" can't retroactively approve something new. Destructive-risk
  actions are excluded from loose assent. Approves via the same HTTP decision
  endpoint the UI button calls, so both paths share one audit trail.
- web/.../InlineApproval.svelte: self-healing poll — a pending approval card
  now picks up being decided via ANY path (chat assent, Ops page, Matrix), not
  just its own button. Previously the banner stayed stuck showing
  Approve/Deny even after the action had already run elsewhere.
- nomos/SOUL.md: `run` is now the general capability ("no fixed menu, only a
  risk gate"); documents chat-assent behavior and the destructive exception.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/policy/command.go

@@ -0,0 +1,133 @@
+package policy
+
+import (
+	"regexp"
+	"strings"
+)
+
+// Risk class names, in escalation order (index = severity). A command's final
+// risk class is the MAX of what the rules compute and what the caller
+// declared — classification can only escalate, never de-escalate, mirroring
+// the signal classifier's "policy can only lower autonomy, never raise it."
+const (
+	RiskReadOnly       = "read_only"
+	RiskReversibleLow  = "reversible_low"
+	RiskConfigMutation = "config_mutation"
+	RiskDestructive    = "destructive"
+)
+
+var riskOrder = map[string]int{
+	RiskReadOnly:       0,
+	RiskReversibleLow:  1,
+	RiskConfigMutation: 2,
+	RiskDestructive:    3,
+}
+
+func riskRank(r string) int {
+	if n, ok := riskOrder[r]; ok {
+		return n
+	}
+	return riskOrder[RiskConfigMutation] // unknown declared risk: assume the safer-to-gate default
+}
+
+// destructivePatterns match commands that must always be treated as
+// destructive, regardless of what the caller declares. Irreversible,
+// data-loss, or fleet-wide-impact operations. Matched against the raw
+// command text, case-insensitive.
+var destructivePatterns = []*regexp.Regexp{
+	regexp.MustCompile(`(?i)\brm\s+.*-[a-zA-Z]*r[a-zA-Z]*f|\brm\s+.*-[a-zA-Z]*f[a-zA-Z]*r`), // rm -rf / rm -fr (any flag order)
+	regexp.MustCompile(`(?i)\bdd\s+.*of=`),
+	regexp.MustCompile(`(?i)\bmkfs(\.\w+)?\b`),
+	regexp.MustCompile(`(?i)\bwipefs\b`),
+	regexp.MustCompile(`(?i)\bshred\b`),
+	regexp.MustCompile(`(?i)\bpct\s+destroy\b`),
+	regexp.MustCompile(`(?i)\bqm\s+destroy\b`),
+	regexp.MustCompile(`(?i)\bzpool\s+destroy\b`),
+	regexp.MustCompile(`(?i)\blvremove\b|\bvgremove\b|\bpvremove\b`),
+	regexp.MustCompile(`(?i)\bdrop\s+(table|database|schema)\b`),
+	regexp.MustCompile(`(?i)\btruncate\s+table\b`),
+	regexp.MustCompile(`(?i)>\s*/dev/(sd|nvme|vd|hd)`),
+	regexp.MustCompile(`(?i)\bshutdown\b|\breboot\b|\bhalt\b|\bpoweroff\b`),
+	regexp.MustCompile(`(?i)\bformat\b.*\b(disk|partition|volume)\b`),
+	regexp.MustCompile(`:\(\)\s*\{.*:\|:.*\}\s*;\s*:`), // fork bomb
+	regexp.MustCompile(`(?i)\bchmod\s+-R\s+000\b|\bchmod\s+000\s+/`),
+	regexp.MustCompile(`(?i)\biptables\s+-F\b|\bufw\s+disable\b`), // wipes firewall
+	// secret/credential exfiltration or piping a remote script straight into a root shell
+	regexp.MustCompile(`(?i)\bcurl\b.*\|\s*(sudo\s+)?(ba)?sh\b`),
+	regexp.MustCompile(`(?i)\bwget\b.*\|\s*(sudo\s+)?(ba)?sh\b`),
+	regexp.MustCompile(`(?i)\bcat\s+.*(id_rsa|id_ed25519|\.pem|shadow|\.age)\b`),
+}
+
+// readOnlyLeadPattern matches the leading command word (after env-var
+// prefixes and a leading sudo) against a small allowlist of verbs that are
+// safe to auto-run unattended: they inspect state and cannot mutate it.
+// Compound commands (&&, ;, |, $(), backticks) are excluded from this fast
+// path below — only a single simple command can qualify.
+var readOnlyLeadPattern = regexp.MustCompile(
+	`^(cat|less|head|tail|ls|stat|file|du|df|free|uptime|uname|hostname|whoami|id|ip|ss|netstat|ping|` +
+		`journalctl|dmesg|ps|top|htop|env|printenv|echo|which|whereis|` +
+		`systemctl\s+(status|is-active|is-enabled|is-failed|list-units)|` +
+		`docker\s+(ps|images|inspect|logs|version|info)|` +
+		`pct\s+(status|config|list)|qm\s+(status|config|list)|pvesh\s+get|` +
+		`git\s+(status|log|diff|show|branch|remote)|` +
+		`curl\s+-.*-I\b|curl\s+.*--head\b)\b`)
+
+// compoundOpPattern matches shell operators that chain or substitute
+// commands. A "read-only lead verb" only qualifies a command for the
+// read_only fast path when the WHOLE command is simple — otherwise a
+// compound like "cat file && rm -rf /" would slip through on its first verb.
+var compoundOpPattern = regexp.MustCompile("[;&|`]|\\$\\(")
+
+// ClassifyCommand scores an arbitrary shell command for the general `run`
+// primitive. It combines a rule-based verdict (destructive denylist first,
+// then a read-only allowlist for simple inspection commands) with the
+// caller's declared risk, and returns the more severe of the two — the
+// classifier may only escalate, never de-escalate, so a model that
+// under-declares risk (or an adversarial prompt) cannot talk its way past a
+// genuinely dangerous command. Anything not matched by either rule defaults
+// to config_mutation (escalate), per "when in doubt, escalate."
+func ClassifyCommand(command, declaredRisk string) string {
+	computed := computeCommandRisk(command)
+	if declaredRisk == "" {
+		return computed // no declaration to escalate with; computed's own escalate-by-default already applies
+	}
+	declared := normalizeRisk(declaredRisk)
+	if riskRank(declared) > riskRank(computed) {
+		return declared
+	}
+	return computed
+}
+
+func normalizeRisk(r string) string {
+	if _, ok := riskOrder[r]; ok {
+		return r
+	}
+	return RiskConfigMutation
+}
+
+func computeCommandRisk(command string) string {
+	cmd := strings.TrimSpace(command)
+	if cmd == "" {
+		return RiskConfigMutation
+	}
+
+	for _, p := range destructivePatterns {
+		if p.MatchString(cmd) {
+			return RiskDestructive
+		}
+	}
+
+	if !compoundOpPattern.MatchString(cmd) {
+		// Strip a leading sudo/env assignment so "sudo cat /x" still matches.
+		probe := cmd
+		probe = regexp.MustCompile(`^sudo\s+`).ReplaceAllString(probe, "")
+		probe = regexp.MustCompile(`^(\w+=\S+\s+)+`).ReplaceAllString(probe, "")
+		if readOnlyLeadPattern.MatchString(probe) {
+			return RiskReadOnly
+		}
+	}
+
+	// Not obviously destructive, not a recognized read-only inspection —
+	// default to the gated tier rather than guessing it's safe.
+	return RiskConfigMutation
+}