diff --git a/Cargo.toml b/Cargo.toml
index 8ec3937c4..d27fbe740 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -87,6 +87,9 @@ members = [
     # in members nor exclude, so `cargo test -p ruvector-agent-memory`
     # could not run at all.
     "crates/ruvector-agent-memory",
+    # StagedWorkspace (arXiv:2608.18050) content-hash state binding
+    # (ADR-318, PIR WP16 ruvnet/RuVector#863).
+    "crates/ruvector-staged-workspace",
     "crates/ruvector-retrieval-receipt",
     "crates/ruvector-gnn-rerank",
     "crates/ruvector-gnn-node",
diff --git a/crates/ruvector-staged-workspace/Cargo.toml b/crates/ruvector-staged-workspace/Cargo.toml
new file mode 100644
index 000000000..2b36e9cd0
--- /dev/null
+++ b/crates/ruvector-staged-workspace/Cargo.toml
@@ -0,0 +1,21 @@
+[package]
+name        = "ruvector-staged-workspace"
+version     = "0.1.0"
+edition     = "2021"
+description = "StagedWorkspace (arXiv:2608.18050) content-hash + revision-id state binding for RuV artifacts: stale views fail closed (ADR-318, PIR WP16)"
+authors     = ["ruvnet", "claude-flow"]
+license     = "MIT OR Apache-2.0"
+repository  = "https://github.com/ruvnet/ruvector"
+keywords    = ["content-hash", "provenance", "workspace", "agent", "ruvector"]
+categories  = ["data-structures"]
+
+[dependencies]
+serde = { workspace = true }
+# The repo's existing RVF-layer SHA-256 (FIPS 180-4, NIST-vector verified,
+# no_std, zero deps). ADR-318 §Decision 1 reuses RVF's canonical-format
+# discipline; the program's canonical receipt contract (ruflo ADR-322C,
+# adopted via ADR-312) specifies SHA-256 — no new hash is introduced.
+rvf-types = { version = "0.2", path = "../rvf/rvf-types", default-features = false }
+
+[dev-dependencies]
+serde_json = { workspace = true }
diff --git a/crates/ruvector-staged-workspace/src/anchor.rs b/crates/ruvector-staged-workspace/src/anchor.rs
new file mode 100644
index 000000000..f224b328b
--- /dev/null
+++ b/crates/ruvector-staged-workspace/src/anchor.rs
@@ -0,0 +1,206 @@
+//! ADR-312 anchoring seam: workspace-state transitions as witness/receipt
+//! records (ADR-318 §Decision 4).
+//!
+//! ADR-312 resolves the program's witness layer as a *shared record schema
+//! plus a cross-layer anchoring contract*: records that must verify across
+//! layers use ruflo ADR-322C's canonical encoding, SHA-256 identity
+//! derivation, and domain-separated Ed25519 signatures
+//! (`Ed25519(domainPrefix || 0x00 || canonicalBytes)`). This module defines
+//! that boundary for workspace-state transitions:
+//!
+//! - [`WorkspaceTransitionRecord`] — the record for one artifact-lineage
+//!   transition, with [`canonical_bytes`](WorkspaceTransitionRecord::canonical_bytes)
+//!   (fixed field order, length-prefixed strings, little-endian integers),
+//!   a SHA-256 [`record_id`](WorkspaceTransitionRecord::record_id) mirroring
+//!   322C's `receiptId = SHA-256(canonical unsigned payload)`, and a
+//!   domain-separated [`signing_preimage`](WorkspaceTransitionRecord::signing_preimage).
+//! - [`TransitionAnchor`] — the trait the workspace emits records through.
+//!   Wiring the full ruflo ADR-322C receipt emission (RFC 8785 JCS +
+//!   Ed25519, ruflo#3066 formal spec) is deliberately out of this slice; a
+//!   real implementation lives behind this trait, the same way
+//!   `ruvector-agent-memory`'s `WitnessSink` stubs its WP8 RVM anchoring.
+//!
+//! **Fail-closed contract**: if `anchor` returns `Err`, the workspace
+//! transition is aborted — "no anchor, no transition", matching ADR-134's
+//! "no witness, no mutation" invariant already enforced by the WP4 ledger.
+
+use serde::{Deserialize, Serialize};
+
+use crate::artifact::ContentHash;
+
+/// Domain-separation prefix for workspace-transition signing preimages,
+/// following ADR-322C's `domainPrefix || 0x00 || canonicalBytes` scheme
+/// (distinct from ruflo's `ruflo/flywheel-receipt/v1` and
+/// `ruflo/flywheel-ledger-head/v1` domains).
+pub const TRANSITION_DOMAIN: &str = "ruv/staged-workspace-transition/v1";
+
+/// Evidence grade, using the three-value vocabulary of the program's
+/// canonical witness/receipt contract (ruflo ADR-322C, adopted via
+/// ADR-312) — the same vocabulary `ruvector-agent-memory::EvidenceGrade`
+/// uses for TARL ledger transitions.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum EvidenceGrade {
+    /// Re-derived from primary data (e.g. the workspace recomputed the
+    /// content hash from the artifact's actual bytes at commit time).
+    Recomputed,
+    /// Backed by a verified cryptographic signature (produced only by a
+    /// real ADR-322C anchor implementation; never by [`NoopAnchor`]).
+    SignatureVerified,
+    /// Asserted without independent recomputation or signature.
+    TrustedAssertion,
+}
+
+impl EvidenceGrade {
+    /// Compact code bound into the canonical encoding
+    /// (1 = recomputed, 2 = signature-verified, 3 = trusted-assertion).
+    pub fn code(self) -> u8 {
+        match self {
+            EvidenceGrade::Recomputed => 1,
+            EvidenceGrade::SignatureVerified => 2,
+            EvidenceGrade::TrustedAssertion => 3,
+        }
+    }
+}
+
+/// One artifact-lineage transition (create or update), as anchored at the
+/// ADR-312 boundary.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct WorkspaceTransitionRecord {
+    /// Workspace-scoped monotonic transition sequence number.
+    pub sequence: u64,
+    /// Wall-clock nanoseconds at commit time.
+    pub timestamp_ns: u64,
+    /// Lineage identity of the artifact that changed.
+    pub artifact_id: String,
+    /// Content hash of the version being superseded (`None` on create).
+    pub prior_hash: Option<ContentHash>,
+    /// Revision id being superseded (`None` on create).
+    pub prior_revision: Option<u64>,
+    /// Content hash of the newly committed version.
+    pub new_hash: ContentHash,
+    /// Revision id of the newly committed version.
+    pub new_revision: u64,
+    /// Identity of the actor that committed the write.
+    pub actor_id: String,
+    /// Evidence grade for the `new_hash` claim. The workspace always sets
+    /// [`EvidenceGrade::Recomputed`]: it derived the hash from the
+    /// artifact's actual bytes, not from a caller's assertion.
+    pub evidence_grade: EvidenceGrade,
+}
+
+impl WorkspaceTransitionRecord {
+    /// Canonical byte encoding: fixed field order, little-endian integers,
+    /// u64-length-prefixed strings, `0x00`/`0x01` option tags. This is the
+    /// crate-local stand-in for ADR-322C's RFC 8785 JCS canonical JSON —
+    /// full JCS shape conformance is the ruflo#3066 follow-up, behind
+    /// [`TransitionAnchor`].
+    pub fn canonical_bytes(&self) -> Vec<u8> {
+        fn put_str(out: &mut Vec<u8>, s: &str) {
+            out.extend_from_slice(&(s.len() as u64).to_le_bytes());
+            out.extend_from_slice(s.as_bytes());
+        }
+        let mut out = Vec::with_capacity(160 + self.artifact_id.len() + self.actor_id.len());
+        out.extend_from_slice(&self.sequence.to_le_bytes());
+        out.extend_from_slice(&self.timestamp_ns.to_le_bytes());
+        put_str(&mut out, &self.artifact_id);
+        match (&self.prior_hash, self.prior_revision) {
+            (Some(h), Some(r)) => {
+                out.push(0x01);
+                out.extend_from_slice(&h.0);
+                out.extend_from_slice(&r.to_le_bytes());
+            }
+            _ => out.push(0x00),
+        }
+        out.extend_from_slice(&self.new_hash.0);
+        out.extend_from_slice(&self.new_revision.to_le_bytes());
+        put_str(&mut out, &self.actor_id);
+        out.push(self.evidence_grade.code());
+        out
+    }
+
+    /// Record identity: `SHA-256(canonical_bytes)`, mirroring ADR-322C's
+    /// `receiptId = SHA-256(JCS(unsigned receipt payload))` derivation.
+    pub fn record_id(&self) -> ContentHash {
+        ContentHash::of(&self.canonical_bytes())
+    }
+
+    /// Signing preimage per ADR-322C's domain-separation scheme:
+    /// `TRANSITION_DOMAIN || 0x00 || canonical_bytes`. A real anchor signs
+    /// this with Ed25519; this slice defines the preimage but does not sign.
+    pub fn signing_preimage(&self) -> Vec<u8> {
+        let canonical = self.canonical_bytes();
+        let mut out = Vec::with_capacity(TRANSITION_DOMAIN.len() + 1 + canonical.len());
+        out.extend_from_slice(TRANSITION_DOMAIN.as_bytes());
+        out.push(0x00);
+        out.extend_from_slice(&canonical);
+        out
+    }
+}
+
+/// Receipt returned by an anchor for one accepted transition record.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct AnchorReceipt {
+    /// The anchored record's identity (`SHA-256` of its canonical bytes).
+    pub record_id: ContentHash,
+    /// How strongly the anchoring itself is evidenced:
+    /// [`EvidenceGrade::TrustedAssertion`] for [`NoopAnchor`];
+    /// [`EvidenceGrade::SignatureVerified`] for a real ADR-322C
+    /// Ed25519-signing anchor.
+    pub grade: EvidenceGrade,
+}
+
+/// Error returned by an anchor that refuses a record. Per the fail-closed
+/// contract, the workspace aborts the transition.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct AnchorError(pub String);
+
+impl core::fmt::Display for AnchorError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        write!(f, "anchor rejected transition record: {}", self.0)
+    }
+}
+
+impl std::error::Error for AnchorError {}
+
+/// The ADR-312 anchoring seam. A workspace-state transition becomes durable
+/// only if its record is accepted here; rejection aborts the transition
+/// ("no anchor, no transition").
+pub trait TransitionAnchor {
+    /// Anchor one transition record, returning a receipt on acceptance.
+    fn anchor(&mut self, record: &WorkspaceTransitionRecord) -> Result<AnchorReceipt, AnchorError>;
+}
+
+/// Accepts every record without signing — grades the anchoring
+/// [`EvidenceGrade::TrustedAssertion`]. The in-process default, mirroring
+/// `ruvector-agent-memory::NoopWitnessSink`; production use requires a real
+/// ADR-322C anchor behind [`TransitionAnchor`].
+#[derive(Debug, Default, Clone, Copy)]
+pub struct NoopAnchor;
+
+impl TransitionAnchor for NoopAnchor {
+    fn anchor(&mut self, record: &WorkspaceTransitionRecord) -> Result<AnchorReceipt, AnchorError> {
+        Ok(AnchorReceipt {
+            record_id: record.record_id(),
+            grade: EvidenceGrade::TrustedAssertion,
+        })
+    }
+}
+
+/// Rejects every record — used to prove the fail-closed "no anchor, no
+/// transition" property in tests.
+#[derive(Debug, Default, Clone)]
+pub struct RejectingAnchor {
+    /// Reason echoed in the [`AnchorError`].
+    pub reason: String,
+}
+
+impl TransitionAnchor for RejectingAnchor {
+    fn anchor(&mut self, _: &WorkspaceTransitionRecord) -> Result<AnchorReceipt, AnchorError> {
+        Err(AnchorError(if self.reason.is_empty() {
+            "rejecting anchor".to_string()
+        } else {
+            self.reason.clone()
+        }))
+    }
+}
diff --git a/crates/ruvector-staged-workspace/src/artifact.rs b/crates/ruvector-staged-workspace/src/artifact.rs
new file mode 100644
index 000000000..a254d26e2
--- /dev/null
+++ b/crates/ruvector-staged-workspace/src/artifact.rs
@@ -0,0 +1,78 @@
+//! Artifact identity: content hash + revision id (ADR-318 §Decision 1).
+
+use core::fmt;
+use serde::{Deserialize, Serialize};
+
+/// SHA-256 content hash of an artifact's canonical byte representation.
+///
+/// Computed with the repo's existing RVF-layer SHA-256
+/// ([`rvf_types::sha256`], FIPS 180-4, verified against NIST vectors) — the
+/// same SHA-256 the program's canonical receipt/witness contract (ruflo
+/// ADR-322C, adopted via ADR-312) specifies. ADR-318 explicitly reuses the
+/// existing hashing discipline rather than introducing a new hash.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct ContentHash(pub [u8; 32]);
+
+impl ContentHash {
+    /// Hash `content` (the artifact's canonical bytes).
+    pub fn of(content: &[u8]) -> Self {
+        Self(rvf_types::sha256::sha256(content))
+    }
+
+    /// Lowercase hex rendering (64 chars).
+    pub fn to_hex(&self) -> String {
+        let mut s = String::with_capacity(64);
+        for b in self.0 {
+            use core::fmt::Write;
+            let _ = write!(s, "{b:02x}");
+        }
+        s
+    }
+}
+
+impl fmt::Display for ContentHash {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_hex())
+    }
+}
+
+/// A reference to one **exact version** of one artifact.
+///
+/// This is the binding unit of ADR-318: every downstream reference (parser
+/// result, tool call, diff, approval, output — see [`crate::ViewKind`])
+/// carries an `ArtifactRef`, i.e. the content hash *and* revision id of the
+/// version it read, not merely the artifact's identity. Modeled on
+/// StagedWorkspace's (arXiv:2608.18050) binding of parsed records and review
+/// diffs to native-file content hashes.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct ArtifactRef {
+    /// Stable identity of the artifact's lineage (e.g. a workspace path or
+    /// RVF record id). Identity alone is NOT a version reference.
+    pub artifact_id: String,
+    /// SHA-256 of the exact version's canonical bytes.
+    pub content_hash: ContentHash,
+    /// Monotonic revision counter scoped to this artifact's lineage
+    /// (starts at 1 for the first committed version).
+    pub revision_id: u64,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hash_matches_known_sha256_vector() {
+        // NIST vector: SHA-256("abc")
+        let h = ContentHash::of(b"abc");
+        assert_eq!(
+            h.to_hex(),
+            "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
+        );
+    }
+
+    #[test]
+    fn display_is_hex() {
+        let h = ContentHash::of(b"");
+        assert_eq!(format!("{h}").len(), 64);
+    }
+}
diff --git a/crates/ruvector-staged-workspace/src/lib.rs b/crates/ruvector-staged-workspace/src/lib.rs
new file mode 100644
index 000000000..c37fbfe96
--- /dev/null
+++ b/crates/ruvector-staged-workspace/src/lib.rs
@@ -0,0 +1,58 @@
+//! # ruvector-staged-workspace
+//!
+//! Content-hash + revision-id state binding for RuV artifacts, implementing
+//! the **StagedWorkspace (arXiv:2608.18050)** pattern as a RuV invariant
+//! per **ADR-318** (`docs/adr/ADR-318-stagedworkspace-content-hash-state-binding.md`,
+//! PIR WP16, ruvnet/RuVector#863).
+//!
+//! ## The invariant (ADR-318 §Decision)
+//!
+//! 1. **Every artifact gets a content hash and a revision id at write time.**
+//!    The hash is SHA-256 over the artifact's canonical byte representation,
+//!    computed with the repo's existing RVF-layer implementation
+//!    ([`rvf_types::sha256`]) — the same SHA-256 the program's canonical
+//!    receipt contract (ruflo ADR-322C, adopted via ADR-312) specifies.
+//! 2. **Every downstream reference binds to that exact hash**, not just the
+//!    artifact's identity: a [`StagedView`] records the [`ArtifactRef`]
+//!    (hash + revision) of the exact version it was derived from, for all
+//!    five view kinds ADR-318 enumerates ([`ViewKind`]: parser result, tool
+//!    call, diff, approval, output).
+//! 3. **Stale state is automatically invalid.** When the workspace's live
+//!    hash for an artifact no longer matches a view's recorded hash,
+//!    [`WorkspaceState::validate`] and [`WorkspaceState::execute`] reject
+//!    the view with a hard error — a structural, fail-closed rejection at
+//!    read time, never a soft warning.
+//! 4. Workspace-state transitions are anchored through the **ADR-312 seam**
+//!    ([`TransitionAnchor`]): each commit produces a
+//!    [`WorkspaceTransitionRecord`] with a canonical byte encoding, a
+//!    SHA-256 record id (mirroring ADR-322C's `receiptId = SHA-256(canonical
+//!    payload)` identity derivation), and a domain-separated signing
+//!    preimage (`domain || 0x00 || canonicalBytes`, ADR-322C's scheme).
+//!    Per the "no anchor, no transition" discipline (the same fail-closed
+//!    posture as ADR-134's "no witness, no mutation" in
+//!    `ruvector-agent-memory`), an anchor rejection aborts the commit.
+//!
+//! ## Preprint-reproduction rule (read before citing numbers)
+//!
+//! StagedWorkspace (arXiv:2608.18050) reports +8.3–12.1pp OfficeQA Pass@1
+//! for dual parsed/native access on the paper's own models and reference
+//! implementation, **which is not publicly released** ("Under Review", no
+//! repo — verified in `06-wave2-evidence-review.md` §5). This crate is a
+//! first-party implementation from the paper's description. **The paper's
+//! figure is NOT claimed here**: per ADR-318 §Decision 5 and ADR-306,
+//! promotion requires this program's own `research-gate`-recomputed delta on
+//! an internal OfficeQA-equivalent task set — a future benchmark deliverable,
+//! not part of this slice.
+
+pub mod anchor;
+pub mod artifact;
+pub mod view;
+pub mod workspace;
+
+pub use anchor::{
+    AnchorError, AnchorReceipt, EvidenceGrade, NoopAnchor, RejectingAnchor, TransitionAnchor,
+    WorkspaceTransitionRecord, TRANSITION_DOMAIN,
+};
+pub use artifact::{ArtifactRef, ContentHash};
+pub use view::{StagedView, ViewKind};
+pub use workspace::{ViewConflict, WorkspaceError, WorkspaceState};
diff --git a/crates/ruvector-staged-workspace/src/view.rs b/crates/ruvector-staged-workspace/src/view.rs
new file mode 100644
index 000000000..5a630052d
--- /dev/null
+++ b/crates/ruvector-staged-workspace/src/view.rs
@@ -0,0 +1,60 @@
+//! Staged views: parsed/derived state bound to the exact artifact version it
+//! came from (ADR-318 §Decision 2).
+
+use serde::{Deserialize, Serialize};
+
+use crate::artifact::{ArtifactRef, ContentHash};
+
+/// The five downstream-reference kinds ADR-318 enumerates. Each one is a
+/// piece of derived state that reads or acts on an artifact and must record
+/// the content hash (and revision id) of the exact version it used.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+#[serde(rename_all = "kebab-case")]
+pub enum ViewKind {
+    /// A parser's structured output over the artifact's native bytes
+    /// (StagedWorkspace's "parsed records").
+    ParserResult,
+    /// A tool call whose input read the artifact.
+    ToolCall,
+    /// A review diff computed against the artifact
+    /// (StagedWorkspace's "review diffs").
+    Diff,
+    /// An approval decision made while looking at the artifact.
+    Approval,
+    /// A generated output derived from the artifact.
+    Output,
+}
+
+impl ViewKind {
+    /// All five kinds, for exhaustive iteration in tests and audits.
+    pub const ALL: [ViewKind; 5] = [
+        ViewKind::ParserResult,
+        ViewKind::ToolCall,
+        ViewKind::Diff,
+        ViewKind::Approval,
+        ViewKind::Output,
+    ];
+}
+
+/// A parsed/derived view bound to the exact artifact version it came from.
+///
+/// A `StagedView` is valid only while the workspace's live head for
+/// `artifact.artifact_id` still has `artifact.content_hash`. The moment the
+/// artifact changes, every view bound to the old hash is stale by
+/// construction and is rejected fail-closed by
+/// [`crate::WorkspaceState::validate`] / [`crate::WorkspaceState::execute`].
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct StagedView {
+    /// Workspace-scoped monotonic view id (audit handle; not the binding —
+    /// the binding is `artifact`).
+    pub view_id: u64,
+    /// Which of ADR-318's five reference kinds this view is.
+    pub kind: ViewKind,
+    /// The exact artifact version (hash + revision) this view was derived
+    /// from. This is the ADR-318 binding.
+    pub artifact: ArtifactRef,
+    /// SHA-256 of the view's own derived payload (parser output, diff text,
+    /// approval record, ...), so the view's content is itself
+    /// content-addressed and receipt-referenceable.
+    pub payload_hash: ContentHash,
+}
diff --git a/crates/ruvector-staged-workspace/src/workspace.rs b/crates/ruvector-staged-workspace/src/workspace.rs
new file mode 100644
index 000000000..3eace3406
--- /dev/null
+++ b/crates/ruvector-staged-workspace/src/workspace.rs
@@ -0,0 +1,265 @@
+//! Workspace state: artifact lineages, view staging, and the fail-closed
+//! staleness gate (ADR-318 §Decision 3).
+
+use std::collections::HashMap;
+use std::time::{SystemTime, UNIX_EPOCH};
+
+use crate::anchor::{AnchorReceipt, EvidenceGrade, TransitionAnchor, WorkspaceTransitionRecord};
+use crate::artifact::{ArtifactRef, ContentHash};
+use crate::view::{StagedView, ViewKind};
+
+/// The bound-vs-head detail of a rejected view (boxed inside
+/// [`WorkspaceError`] to keep the error type small on the `Ok` path).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ViewConflict {
+    /// Lineage the view referenced.
+    pub artifact_id: String,
+    /// The exact version the view was derived from.
+    pub bound: ArtifactRef,
+    /// The artifact's current live head.
+    pub head: ArtifactRef,
+}
+
+/// Errors returned by [`WorkspaceState`]. Every variant is a hard rejection:
+/// per ADR-318, staleness and binding violations are never soft warnings.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum WorkspaceError {
+    /// The referenced artifact lineage does not exist in this workspace.
+    UnknownArtifact(String),
+    /// The view is bound to a content hash that is no longer the artifact's
+    /// live head — the ADR-318 §Decision 3 structural staleness rejection.
+    /// Any operation carrying this view must recompute against the head.
+    StaleView(Box<ViewConflict>),
+    /// The view's hash matches the live head but its revision id does not —
+    /// a corrupt or forged binding, rejected outright.
+    BindingMismatch(Box<ViewConflict>),
+    /// The ADR-312 anchor refused the transition record; per the
+    /// "no anchor, no transition" contract the commit was NOT applied.
+    AnchorRejected(String),
+}
+
+impl core::fmt::Display for WorkspaceError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            WorkspaceError::UnknownArtifact(id) => write!(f, "unknown artifact lineage {id:?}"),
+            WorkspaceError::StaleView(c) => write!(
+                f,
+                "stale view of {:?}: bound to {} (rev {}), live head is {} (rev {}) — recompute required",
+                c.artifact_id,
+                c.bound.content_hash,
+                c.bound.revision_id,
+                c.head.content_hash,
+                c.head.revision_id
+            ),
+            WorkspaceError::BindingMismatch(c) => write!(
+                f,
+                "binding mismatch for {:?}: view claims (hash {}, rev {}), head is (hash {}, rev {})",
+                c.artifact_id,
+                c.bound.content_hash,
+                c.bound.revision_id,
+                c.head.content_hash,
+                c.head.revision_id
+            ),
+            WorkspaceError::AnchorRejected(msg) => {
+                write!(f, "anchor rejected transition (commit aborted): {msg}")
+            }
+        }
+    }
+}
+
+impl std::error::Error for WorkspaceError {}
+
+/// One artifact's lineage: its live head and the full hash history.
+#[derive(Debug, Clone)]
+struct ArtifactLineage {
+    head: ArtifactRef,
+    /// Every committed hash, oldest first; last entry equals `head.content_hash`.
+    history: Vec<ContentHash>,
+}
+
+/// The workspace: artifact lineages plus the validation gate that makes
+/// stale views structurally invalid.
+///
+/// Generic over the [`TransitionAnchor`] so callers (WP15's acceptance
+/// harness, RVF/RVM integrations) can supply a real ADR-312/322C anchor;
+/// defaults are available via [`WorkspaceState::with_noop_anchor`].
+pub struct WorkspaceState<A: TransitionAnchor> {
+    anchor: A,
+    lineages: HashMap<String, ArtifactLineage>,
+    /// (record, receipt) audit log of every anchored transition.
+    transitions: Vec<(WorkspaceTransitionRecord, AnchorReceipt)>,
+    next_sequence: u64,
+    next_view_id: u64,
+}
+
+impl WorkspaceState<crate::anchor::NoopAnchor> {
+    /// Workspace with the in-process [`crate::anchor::NoopAnchor`].
+    pub fn with_noop_anchor() -> Self {
+        Self::new(crate::anchor::NoopAnchor)
+    }
+}
+
+impl<A: TransitionAnchor> WorkspaceState<A> {
+    /// Create a workspace that anchors every transition through `anchor`.
+    pub fn new(anchor: A) -> Self {
+        Self {
+            anchor,
+            lineages: HashMap::new(),
+            transitions: Vec::new(),
+            next_sequence: 0,
+            next_view_id: 0,
+        }
+    }
+
+    /// Commit a write of `content` to `artifact_id`, assigning a content
+    /// hash and the lineage's next revision id (ADR-318 §Decision 1).
+    ///
+    /// Committing bytes identical to the live head is a no-op returning the
+    /// existing head (no revision bump, no anchor record): the version did
+    /// not change, so no view becomes stale.
+    ///
+    /// The transition record is pushed through the ADR-312 anchor **before**
+    /// the workspace mutates; if the anchor rejects, the commit is aborted
+    /// and the lineage is unchanged ("no anchor, no transition").
+    pub fn commit(
+        &mut self,
+        artifact_id: &str,
+        content: &[u8],
+        actor_id: &str,
+    ) -> Result<ArtifactRef, WorkspaceError> {
+        let new_hash = ContentHash::of(content);
+        let prior = self.lineages.get(artifact_id).map(|l| l.head.clone());
+        if let Some(ref head) = prior {
+            if head.content_hash == new_hash {
+                return Ok(head.clone());
+            }
+        }
+        let new_revision = prior.as_ref().map_or(1, |h| h.revision_id + 1);
+        let record = WorkspaceTransitionRecord {
+            sequence: self.next_sequence,
+            timestamp_ns: now_ns(),
+            artifact_id: artifact_id.to_string(),
+            prior_hash: prior.as_ref().map(|h| h.content_hash),
+            prior_revision: prior.as_ref().map(|h| h.revision_id),
+            new_hash,
+            new_revision,
+            actor_id: actor_id.to_string(),
+            // The workspace derived new_hash from the artifact's actual
+            // bytes above — recomputed, not asserted.
+            evidence_grade: EvidenceGrade::Recomputed,
+        };
+        let receipt = self
+            .anchor
+            .anchor(&record)
+            .map_err(|e| WorkspaceError::AnchorRejected(e.0))?;
+        // Anchor accepted: apply the mutation.
+        self.next_sequence += 1;
+        let head = ArtifactRef {
+            artifact_id: artifact_id.to_string(),
+            content_hash: new_hash,
+            revision_id: new_revision,
+        };
+        let lineage = self
+            .lineages
+            .entry(artifact_id.to_string())
+            .or_insert_with(|| ArtifactLineage {
+                head: head.clone(),
+                history: Vec::new(),
+            });
+        lineage.head = head.clone();
+        lineage.history.push(new_hash);
+        self.transitions.push((record, receipt));
+        Ok(head)
+    }
+
+    /// The artifact's live head (exact current version), if it exists.
+    pub fn head(&self, artifact_id: &str) -> Option<&ArtifactRef> {
+        self.lineages.get(artifact_id).map(|l| &l.head)
+    }
+
+    /// Derive a view of `artifact_id`'s **current** version, binding it to
+    /// the head's exact hash + revision (ADR-318 §Decision 2). `payload` is
+    /// the view's own derived content (parser output, diff text, ...).
+    pub fn stage_view(
+        &mut self,
+        kind: ViewKind,
+        artifact_id: &str,
+        payload: &[u8],
+    ) -> Result<StagedView, WorkspaceError> {
+        let head = self
+            .lineages
+            .get(artifact_id)
+            .map(|l| l.head.clone())
+            .ok_or_else(|| WorkspaceError::UnknownArtifact(artifact_id.to_string()))?;
+        let view = StagedView {
+            view_id: self.next_view_id,
+            kind,
+            artifact: head,
+            payload_hash: ContentHash::of(payload),
+        };
+        self.next_view_id += 1;
+        Ok(view)
+    }
+
+    /// Validate that `view` is still current: its bound content hash must
+    /// equal the artifact's live head hash (and the revision ids must
+    /// agree). Any mismatch is a hard rejection (ADR-318 §Decision 3).
+    pub fn validate(&self, view: &StagedView) -> Result<(), WorkspaceError> {
+        let id = &view.artifact.artifact_id;
+        let head = self
+            .lineages
+            .get(id)
+            .map(|l| &l.head)
+            .ok_or_else(|| WorkspaceError::UnknownArtifact(id.clone()))?;
+        let hash_ok = view.artifact.content_hash == head.content_hash;
+        let rev_ok = view.artifact.revision_id == head.revision_id;
+        match (hash_ok, rev_ok) {
+            (true, true) => Ok(()),
+            (false, _) => Err(WorkspaceError::StaleView(Box::new(ViewConflict {
+                artifact_id: id.clone(),
+                bound: view.artifact.clone(),
+                head: head.clone(),
+            }))),
+            (true, false) => Err(WorkspaceError::BindingMismatch(Box::new(ViewConflict {
+                artifact_id: id.clone(),
+                bound: view.artifact.clone(),
+                head: head.clone(),
+            }))),
+        }
+    }
+
+    /// Run `op` only if `view` is still current — the fail-closed gate.
+    ///
+    /// If validation fails, `op` is **never invoked** and the error is
+    /// returned: an operation carrying a stale view cannot execute
+    /// (ADR-318 §Decision 3, "enforced structurally at read time").
+    pub fn execute<T>(
+        &self,
+        view: &StagedView,
+        op: impl FnOnce(&ArtifactRef) -> T,
+    ) -> Result<T, WorkspaceError> {
+        self.validate(view)?;
+        // `validate` guaranteed the lineage exists and matches.
+        let head = self
+            .head(&view.artifact.artifact_id)
+            .expect("validated lineage must exist");
+        Ok(op(head))
+    }
+
+    /// Audit log of every anchored transition, oldest first.
+    pub fn transitions(&self) -> &[(WorkspaceTransitionRecord, AnchorReceipt)] {
+        &self.transitions
+    }
+
+    /// Full committed hash history for an artifact, oldest first.
+    pub fn history(&self, artifact_id: &str) -> Option<&[ContentHash]> {
+        self.lineages.get(artifact_id).map(|l| l.history.as_slice())
+    }
+}
+
+fn now_ns() -> u64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0)
+}
diff --git a/crates/ruvector-staged-workspace/tests/invariant.rs b/crates/ruvector-staged-workspace/tests/invariant.rs
new file mode 100644
index 000000000..2c05152d2
--- /dev/null
+++ b/crates/ruvector-staged-workspace/tests/invariant.rs
@@ -0,0 +1,234 @@
+//! ADR-318 invariant tests: hash binding round-trips, mutation invalidates
+//! bound views, stale-view operations fail closed, current-view operations
+//! succeed, and anchor rejection aborts commits.
+//!
+//! Benchmark note (preprint-reproduction rule): StagedWorkspace
+//! (arXiv:2608.18050) reports +8.3-12.1pp OfficeQA Pass@1 for its own
+//! models/implementation. That figure is NOT asserted by any test here; the
+//! program's own delta on an internal OfficeQA-equivalent task set is a
+//! future `research-gate` benchmark deliverable (ADR-318 §Decision 5).
+
+use std::cell::Cell;
+
+use ruvector_staged_workspace::{
+    ArtifactRef, ContentHash, EvidenceGrade, RejectingAnchor, StagedView, ViewKind, WorkspaceError,
+    WorkspaceState, TRANSITION_DOMAIN,
+};
+
+const DOC: &str = "reports/q3.md";
+
+// ── 1. Hash binding round-trips ─────────────────────────────────────────────
+
+#[test]
+fn commit_binds_content_hash_and_revision() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    let head = ws.commit(DOC, b"v1 bytes", "agent-a").unwrap();
+    // The recorded hash is exactly SHA-256 of the committed bytes,
+    // independently recomputable.
+    assert_eq!(head.content_hash, ContentHash::of(b"v1 bytes"));
+    assert_eq!(head.revision_id, 1);
+    assert_eq!(ws.head(DOC), Some(&head));
+}
+
+#[test]
+fn staged_view_serde_round_trip_preserves_binding() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    let view = ws
+        .stage_view(ViewKind::ParserResult, DOC, b"parsed")
+        .unwrap();
+    let json = serde_json::to_string(&view).unwrap();
+    let back: StagedView = serde_json::from_str(&json).unwrap();
+    assert_eq!(back, view);
+    // The deserialized view still validates against the live workspace.
+    ws.validate(&back).unwrap();
+}
+
+#[test]
+fn identical_content_commit_is_idempotent() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    let first = ws.commit(DOC, b"same", "agent-a").unwrap();
+    let view = ws.stage_view(ViewKind::Output, DOC, b"out").unwrap();
+    let second = ws.commit(DOC, b"same", "agent-a").unwrap();
+    // No version change: same ref, no new transition, view stays current.
+    assert_eq!(first, second);
+    assert_eq!(ws.transitions().len(), 1);
+    ws.validate(&view).unwrap();
+}
+
+#[test]
+fn revisions_are_monotonic_and_history_is_kept() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    for (i, content) in [b"a".as_ref(), b"b", b"c"].into_iter().enumerate() {
+        let head = ws.commit(DOC, content, "agent-a").unwrap();
+        assert_eq!(head.revision_id, i as u64 + 1);
+    }
+    let history = ws.history(DOC).unwrap();
+    assert_eq!(history.len(), 3);
+    assert_eq!(history[2], ContentHash::of(b"c"));
+}
+
+// ── 2. Mutation invalidates every view bound to the old hash ────────────────
+
+#[test]
+fn mutation_invalidates_all_five_view_kinds() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    // Bind one view of every kind ADR-318 enumerates to revision 1.
+    let views: Vec<StagedView> = ViewKind::ALL
+        .iter()
+        .map(|&kind| ws.stage_view(kind, DOC, b"derived").unwrap())
+        .collect();
+    for v in &views {
+        ws.validate(v).unwrap(); // current before the mutation
+    }
+    // The workspace changes...
+    ws.commit(DOC, b"v2", "agent-b").unwrap();
+    // ...and every view bound to the old hash is now structurally stale.
+    for v in &views {
+        match ws.validate(v) {
+            Err(WorkspaceError::StaleView(conflict)) => {
+                assert_eq!(conflict.bound.content_hash, ContentHash::of(b"v1"));
+                assert_eq!(conflict.head.content_hash, ContentHash::of(b"v2"));
+                assert_eq!(conflict.head.revision_id, 2);
+            }
+            other => panic!("expected StaleView for {:?}, got {other:?}", v.kind),
+        }
+    }
+}
+
+// ── 3. Fail-closed proof: a stale-view operation never runs ─────────────────
+
+#[test]
+fn stale_view_operation_fails_closed_op_never_runs() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    let view = ws
+        .stage_view(ViewKind::Approval, DOC, b"approve v1")
+        .unwrap();
+    ws.commit(DOC, b"v2", "agent-b").unwrap();
+
+    let ran = Cell::new(false);
+    let result = ws.execute(&view, |_| ran.set(true));
+    assert!(matches!(result, Err(WorkspaceError::StaleView(_))));
+    // The operation body was never invoked: stale state is rejected before
+    // execution, not after.
+    assert!(!ran.get(), "operation ran against a stale view");
+}
+
+#[test]
+fn current_view_operation_succeeds() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    let view = ws
+        .stage_view(ViewKind::ToolCall, DOC, b"tool input")
+        .unwrap();
+    let seen_rev = ws.execute(&view, |head| head.revision_id).unwrap();
+    assert_eq!(seen_rev, 1);
+}
+
+#[test]
+fn unknown_artifact_view_fails_closed() {
+    let ws = WorkspaceState::with_noop_anchor();
+    let forged = StagedView {
+        view_id: 0,
+        kind: ViewKind::Diff,
+        artifact: ArtifactRef {
+            artifact_id: "no/such/artifact".into(),
+            content_hash: ContentHash::of(b"x"),
+            revision_id: 1,
+        },
+        payload_hash: ContentHash::of(b"diff"),
+    };
+    assert!(matches!(
+        ws.validate(&forged),
+        Err(WorkspaceError::UnknownArtifact(_))
+    ));
+    let ran = Cell::new(false);
+    assert!(ws.execute(&forged, |_| ran.set(true)).is_err());
+    assert!(!ran.get());
+}
+
+#[test]
+fn matching_hash_with_wrong_revision_is_rejected_as_binding_mismatch() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    let mut view = ws.stage_view(ViewKind::Output, DOC, b"out").unwrap();
+    view.artifact.revision_id = 99; // forged revision, correct hash
+    assert!(matches!(
+        ws.validate(&view),
+        Err(WorkspaceError::BindingMismatch(_))
+    ));
+}
+
+// ── 4. ADR-312 anchoring seam ───────────────────────────────────────────────
+
+#[test]
+fn anchor_rejection_aborts_commit_no_anchor_no_transition() {
+    let mut ws = WorkspaceState::new(RejectingAnchor {
+        reason: "ledger offline".into(),
+    });
+    let err = ws.commit(DOC, b"v1", "agent-a").unwrap_err();
+    assert!(matches!(err, WorkspaceError::AnchorRejected(ref m) if m == "ledger offline"));
+    // The mutation was NOT applied: no head, no history, no transitions.
+    assert!(ws.head(DOC).is_none());
+    assert!(ws.history(DOC).is_none());
+    assert!(ws.transitions().is_empty());
+}
+
+#[test]
+fn transitions_carry_receipts_with_record_ids_and_evidence_grades() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    ws.commit(DOC, b"v2", "agent-b").unwrap();
+    let transitions = ws.transitions();
+    assert_eq!(transitions.len(), 2);
+
+    let (create, create_receipt) = &transitions[0];
+    assert_eq!(create.prior_hash, None);
+    assert_eq!(create.new_revision, 1);
+    // The workspace recomputed the hash from primary bytes.
+    assert_eq!(create.evidence_grade, EvidenceGrade::Recomputed);
+    // Receipt identity is the 322C-style SHA-256 of the canonical record.
+    assert_eq!(create_receipt.record_id, create.record_id());
+    // NoopAnchor cannot claim a signature.
+    assert_eq!(create_receipt.grade, EvidenceGrade::TrustedAssertion);
+
+    let (update, _) = &transitions[1];
+    assert_eq!(update.prior_hash, Some(ContentHash::of(b"v1")));
+    assert_eq!(update.prior_revision, Some(1));
+    assert_eq!(update.new_hash, ContentHash::of(b"v2"));
+    assert_eq!(update.new_revision, 2);
+}
+
+#[test]
+fn record_id_is_deterministic_and_field_sensitive() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    ws.commit("other.md", b"v1", "agent-a").unwrap();
+    let (a, _) = &ws.transitions()[0];
+    let (b, _) = &ws.transitions()[1];
+    assert_eq!(
+        a.record_id(),
+        a.record_id(),
+        "record_id must be deterministic"
+    );
+    assert_ne!(
+        a.record_id(),
+        b.record_id(),
+        "records differing in any field must differ in identity"
+    );
+}
+
+#[test]
+fn signing_preimage_is_domain_separated() {
+    let mut ws = WorkspaceState::with_noop_anchor();
+    ws.commit(DOC, b"v1", "agent-a").unwrap();
+    let (record, _) = &ws.transitions()[0];
+    let preimage = record.signing_preimage();
+    let domain = TRANSITION_DOMAIN.as_bytes();
+    // ADR-322C scheme: domain || 0x00 || canonicalBytes.
+    assert_eq!(&preimage[..domain.len()], domain);
+    assert_eq!(preimage[domain.len()], 0x00);
+    assert_eq!(&preimage[domain.len() + 1..], &record.canonical_bytes()[..]);
+}