provenance: env var based tagging via POC_PROVENANCE

upsert() now checks POC_PROVENANCE env var for provenance label,
falling back to Manual. This lets external callers (Claude sessions,
scripts) tag writes without needing to use the internal
upsert_provenance() API.

Add from_env() and from_label() to Provenance for parsing.

src/store/ops.rs

@@ -29,8 +29,12 @@ impl Store {
 
     /// Upsert a node: update if exists (and content changed), create if not.
     /// Returns: "created", "updated", or "unchanged".
+    ///
+    /// Provenance is determined by the POC_PROVENANCE env var if set,
+    /// otherwise defaults to Manual.
     pub fn upsert(&mut self, key: &str, content: &str) -> Result<&'static str, String> {
-        self.upsert_provenance(key, content, Provenance::Manual)
+        let prov = Provenance::from_env().unwrap_or(Provenance::Manual);
+        self.upsert_provenance(key, content, prov)
     }
 
     /// Upsert with explicit provenance (for agent-created nodes).

src/store/types.rs

@@ -248,6 +248,31 @@ pub enum Provenance {
 }
 
 impl Provenance {
+    /// Parse from POC_PROVENANCE env var. Returns None if unset.
+    pub fn from_env() -> Option<Self> {
+        std::env::var("POC_PROVENANCE").ok().and_then(|s| Self::from_label(&s))
+    }
+
+    pub fn from_label(s: &str) -> Option<Self> {
+        Some(match s {
+            "manual"                     => Self::Manual,
+            "journal"                    => Self::Journal,
+            "agent"                      => Self::Agent,
+            "dream"                      => Self::Dream,
+            "derived"                    => Self::Derived,
+            "agent:experience-mine"      => Self::AgentExperienceMine,
+            "agent:knowledge-observation"=> Self::AgentKnowledgeObservation,
+            "agent:knowledge-pattern"    => Self::AgentKnowledgePattern,
+            "agent:knowledge-connector"  => Self::AgentKnowledgeConnector,
+            "agent:knowledge-challenger" => Self::AgentKnowledgeChallenger,
+            "agent:consolidate"          => Self::AgentConsolidate,
+            "agent:digest"               => Self::AgentDigest,
+            "agent:fact-mine"            => Self::AgentFactMine,
+            "agent:decay"                => Self::AgentDecay,
+            _                            => return None,
+        })
+    }
+
     pub fn label(&self) -> &'static str {
         match self {
             Self::Manual                    => "manual",