// persist.el — the soul→engram WRITE-THROUGH boundary (neuron#117).
//
// WHY THIS FILE EXISTS
//   soul.el:571-573 states the ownership rule: "when ENGRAM_URL is set the HTTP
//   Engram owns persistence — the soul must NEVER write to the local snapshot
//   (not the persistence owner)." The soul obeys the NEGATIVE half. The POSITIVE
//   half — how a write made inside the soul actually REACHES the owner — was
//   never built. Sync is pull-only (awareness.el `/api/sync` -> engram_load_merge),
//   so every node the soul creates lives in its process RAM and is shed on
//   restart. Measured live 2026-08-07: soul node_count=102184, engram
//   node_count=79197 — ~23k nodes existing nowhere but RAM.
//
// SCOPE NOTE ON THE PATENT (corrects an earlier internal reading)
//   Engram provisional claims 15-18 describe a delta-sync protocol "with peer
//   Engram instances"; claim 17's pull-then-push sequence is PEER-ENGRAM to
//   PEER-ENGRAM. The soul is NOT a peer Engram — it is a CALLER of the database
//   system API (cf. claim 27, "invoked explicitly by a caller of the database
//   system API"). So claim 17 does not specify a soul↔engram contract and is not
//   cited as authority here. This design is derived from the ownership rule
//   alone: the owner owns the writes, therefore the soul must HAND writes to the
//   owner and must never write the owner's file itself.
//
// THE MECHANISM, AND WHY NOT `POST /api/nodes`
//   The obvious route is the one the persona/boot-counter write-backs already
//   use, POST /api/nodes. It is the wrong instrument here, verified against the
//   live engram binary in a sandbox:
//     - it mints a NEW server-side id (engram_node), so the soul's id and the
//       owner's id diverge — the next /api/sync pull re-imports the node as a
//       DUPLICATE, and any edge referencing the soul's id never resolves;
//     - it accepts only {content, node_type, salience} and drops label, tier,
//       tags, importance, confidence, metadata. A probe posted with tier
//       "Canonical" came back tier "Working", importance 0.5.
//   POST /api/load-merge (Will's own route, el `dc39a61`) is the right one:
//     - engram_load_merge PRESERVES the id and every field;
//     - it dedups nodes by id and edges by (from_id,to_id,relation), so a
//       re-submitted delta is a NO-OP — retry safety is free, and it is the same
//       local-wins semantics the graph already uses;
//     - it calls persist_canonical() — THE OWNER writes its own canonical file.
//       The soul never touches it. The ownership rule is honoured in its
//       strongest form rather than worked around;
//     - it returns real counts {ok, nodes_added, edges_added, node_count},
//       so a receipt can be a MEASUREMENT instead of a fixed success shape.
//
// SPOOL-AND-DRAIN, AND WHY IT IS NOT JUST A DIRECT POST
//   Measured in a sandbox against a 79k-node / 176MB graph (live scale): one
//   load-merge costs ~0.38s, essentially all of it the owner's persist_canonical.
//   A chat turn writes 5-7 nodes; pushing each separately would add ~2.7s per
//   turn. So writes are STAGED and pushed in one coalesced batch.
//   The staging buffer is the FILESYSTEM, not process state, because the soul
//   serves each HTTP connection on its own pthread (el_runtime http_serve_async)
//   and a shared in-process buffer would lose entries to a read-modify-write
//   race — silently, which is the one failure mode this file exists to end.
//   One file per write, named with uuid_v4, is race-free by construction and
//   buys a property a memory buffer cannot: writes that could not be pushed
//   SURVIVE A SOUL CRASH and are drained on the next boot.
//
// WHAT IS DELIBERATELY NOT PUSHED
//   - InternalStateEvent / heartbeat telemetry. Will's own carve-out, stated in
//     engram server.el 8f8ccc9: "48h-pruned, loss-tolerant, ~2/min; snapshotting
//     28MB per heartbeat is waste."
//   NOTE (ours, flagged for Will): we do NOT additionally exclude Working-tier
//   nodes. That exclusion exists in `fb0bb55` to stop the boot counter leaking
//   through the /api/sync PULL; it is about sync backflow, not durability.
//   Applying it here would exclude mem_store — which writes tier "Working" — and
//   mem_store is the single most important durable write path in the soul. Boot
//   seeding reads the canonical file wholesale, so a pushed Working-tier node
//   does survive restart. This is the one classification call this file makes
//   that Will has not ruled on.
//
// WHAT THIS BOUNDARY CANNOT EXPRESS (by construction, not by omission)
//   - engram_strengthen (salience/activation drift): load-merge SKIPS ids that
//     already exist, so it cannot update an existing node. There is no owner-side
//     update/upsert route. Not pushable through any current route; left as a
//     follow-up that needs a change in the engram repo.
//   - engram_forget (hard delete): load-merge is additive and has no delete verb.
//     Propagating deletes would mean DELETE /api/nodes/<id>, a HARD delete at the
//     owner — which scripts/verify-soul-contract.sh section B explicitly fails the
//     build for ("to delete is to supersede/tombstone, never hard-remove"). Local
//     deletes therefore stay local; the TOMBSTONE NODE and its "tombstones" edge
//     (mem_tombstone) are pushed, and that is the sanctioned representation of a
//     deletion in this graph.

// ── Configuration ─────────────────────────────────────────────────────────────

// wt_engram_url — same resolution order as ise_post: env, then the state key
// stashed at boot. NO hardcoded localhost fallback: unlike telemetry, inventing
// a destination for durable data would risk pushing a user's memories at whatever
// happens to be listening on 8742. Empty means "no HTTP owner" -> file mode.
fn wt_engram_url() -> String {
    let env_url: String = env("ENGRAM_URL")
    if !str_eq(env_url, "") { return env_url }
    return state_get("soul_engram_url")
}

fn wt_api_key() -> String {
    let env_key: String = env("ENGRAM_API_KEY")
    if !str_eq(env_key, "") { return env_key }
    return state_get("soul_engram_api_key")
}

// wt_enabled — true only in HTTP-engram mode. In file mode the soul IS the
// persistence owner and every path below is a no-op, so this whole feature is
// inert for genesis/local deployments. That is also what makes it reversible.
fn wt_enabled() -> Bool {
    return !str_eq(wt_engram_url(), "")
}

// wt_spool_dir — where staged deltas live. MUST be readable by the engram
// process: /api/load-merge takes a PATH and the owner opens it itself. Both
// processes are same-host by construction (dev-stack LaunchAgents; the GKE
// image starts engram and soul in one container per entrypoint.sh).
fn wt_spool_dir() -> String {
    let raw: String = env("SOUL_OUTBOX_DIR")
    let dir: String = if str_eq(raw, "") { env("HOME") + "/.neuron/soul-outbox" } else { raw }
    fs_mkdir(dir)
    return dir
}

// ── Helpers ───────────────────────────────────────────────────────────────────

// wt_esc — minimal JSON string escape. Deliberately local rather than reusing
// chat.el's json_safe: persist.el is imported BY memory.el, which is imported by
// chat.el, so depending on chat.el here would be an import cycle.
fn wt_esc(s: String) -> String {
    let s1: String = str_replace(s, "\\", "\\\\")
    let s2: String = str_replace(s1, "\"", "\\\"")
    let s3: String = str_replace(s2, "\n", "\\n")
    let s4: String = str_replace(s3, "\r", "\\r")
    let s5: String = str_replace(s4, "\t", "\\t")
    return s5
}

// wt_durable_class — Will's telemetry carve-out, by node_type. See header.
fn wt_durable_class(node_type: String) -> Bool {
    if str_eq(node_type, "InternalStateEvent") { return false }
    return true
}

// wt_inner — strip the surrounding brackets off a JSON array so several arrays
// can be concatenated into one. Returns "" for "[]" / "" / anything too short.
fn wt_inner(arr: String) -> String {
    let n: Int = str_len(arr)
    if n < 3 { return "" }
    if !str_starts_with(arr, "[") { return "" }
    return str_slice(arr, 1, n - 1)
}

// wt_read — fs_read, plus a MANDATORY reset of the runtime's binary-length hint.
//
// THIS IS NOT OPTIONAL AND MUST NOT BE "SIMPLIFIED" BACK TO A BARE fs_read.
// The pinned runtime (vendor/el-runtime/v1.0.0-20260501) keeps a thread-local
// `_tl_fs_read_len` that fs_read SETS to the file's byte count (so binary files
// can be served with a correct Content-Length) and that http_send_response
// CONSUMES as the Content-Length of the next reply. Nothing else clears it
// except json_get_raw. So any fs_read during request handling that is not
// followed by a json_get_raw makes the NEXT HTTP response advertise the FILE's
// length instead of the body's — and the runtime then sends that many bytes,
// appending whatever adjacent heap memory follows the reply.
//
// Caught here, measured: a /api/neuron/memory reply that should be 86 bytes went
// out as 497, with 411 bytes of this module's own spool paths and log strings
// trailing the JSON. The drain reads spool files mid-request, so this boundary
// is exactly where the landmine gets stepped on.
//
// Upstream el fixed the class in `43636ae` ("pair fs_read length hint with its
// buffer"); that runtime is NOT the one vendored here, and re-pinning the
// runtime is deliberately out of scope for this change. Clearing the hint at
// our own boundary fixes our exposure without touching the pinned C.
// json_get_raw is used as the reset because it is the only builtin in this
// runtime that zeroes the hint, and it does so before any early return.
fn wt_clear_binlen() -> Void {
    let discard: String = json_get_raw("{}", "_wt_reset")
}

fn wt_read(path: String) -> String {
    let data: String = fs_read(path)
    wt_clear_binlen()
    return data
}

// wt_sweep — best-effort removal of the zero-byte husks left by truncation.
// The runtime exposes no unlink builtin, so a drained delta is emptied rather
// than deleted; this reclaims the directory entries.
//
// `-empty` is the safety property, not an optimisation: the command is
// STRUCTURALLY INCAPABLE of removing a delta that still has content, so it can
// never destroy a pending write even if it runs concurrently with a stage.
// Only the directory path is interpolated (never a filename), and it is quoted.
// The exit code is ignored — an un-swept husk costs one directory entry.
fn wt_sweep(dir: String) -> Void {
    if str_eq(dir, "") { return }
    if str_contains(dir, "'") { return }
    exec_command("find '" + dir + "' -maxdepth 1 -name 'wt*.json' -empty -delete 2>/dev/null")
}

// ── Staging ───────────────────────────────────────────────────────────────────

// wt_stage — write ONE delta file. uuid_v4 in the name makes concurrent stagers
// collision-free without any lock. Returns true if the delta is on disk.
fn wt_stage(nodes_json: String, edges_json: String) -> Bool {
    let dir: String = wt_spool_dir()
    if str_eq(dir, "") { return false }
    let payload: String = "{\"nodes\":" + nodes_json + ",\"edges\":" + edges_json + "}"
    let path: String = dir + "/wt-" + uuid_v4() + ".json"
    fs_write(path, payload)
    // Read-back-verify the stage itself. A stage that did not land is a write we
    // would otherwise believe was queued — exactly the hallucinated-save class.
    if str_eq(wt_read(path), "") {
        println("[persist] wt_stage: FAILED to write spool file " + path + " — delta not queued")
        return false
    }
    return true
}

// ── The write boundary ────────────────────────────────────────────────────────

// wt_node — create a node locally AND queue it for the persistence owner.
// Same signature and same return contract as engram_node_full ("" on failure),
// so converting a call site is a rename and nothing else.
fn wt_node(content: String, node_type: String, label: String,
           salience: Float, importance: Float, confidence: Float,
           tier: String, tags: String) -> String {
    let id: String = engram_node_full(content, node_type, label,
                                      salience, importance, confidence,
                                      tier, tags)
    if str_eq(id, "") { return "" }
    // engram_get_node_json emits the SAME record shape engram_save writes (minus
    // the embedding vector, which the owner backfills lazily), so the read-back
    // doubles as the delta payload — no second serialization to drift.
    let rec: String = engram_get_node_json(id)
    if str_eq(rec, "") || str_eq(rec, "{}") {
        println("[persist] wt_node: local write did not read back, id=" + id + " label=" + label)
        return ""
    }
    if wt_enabled() && wt_durable_class(node_type) {
        wt_stage("[" + rec + "]", "[]")
    }
    return id
}

// wt_edge — create an edge locally AND queue it. Mirrors engram_connect.
//
// The edge id is freshly generated rather than read back: the runtime exposes no
// "id of the edge I just created" accessor, and the owner dedups edges by
// (from_id,to_id,relation), never by id — so the id is not load-bearing. The
// consequence, stated plainly: the soul's copy and the owner's copy of the same
// edge carry different edge ids. Nothing in either codebase looks an edge up by
// id (neighbors traversal scans from_id/to_id), so this is cosmetic.
fn wt_edge(from_id: String, to_id: String, weight: Float, relation: String) -> Void {
    engram_connect(from_id, to_id, weight, relation)
    if !wt_enabled() { return }
    if str_eq(from_id, "") || str_eq(to_id, "") { return }
    let ts: Int = time_now()
    let rec: String = "{\"id\":\"" + uuid_v4() + "\""
        + ",\"from_id\":\"" + wt_esc(from_id) + "\""
        + ",\"to_id\":\"" + wt_esc(to_id) + "\""
        + ",\"relation\":\"" + wt_esc(relation) + "\""
        + ",\"metadata\":\"{}\""
        + ",\"weight\":" + float_to_str(weight)
        + ",\"confidence\":1"
        + ",\"created_at\":" + int_to_str(ts)
        + ",\"updated_at\":" + int_to_str(ts)
        + ",\"last_fired\":0,\"inhibitory\":0,\"layer_id\":1}"
    wt_stage("[]", "[" + rec + "]")
}

// ── The drain ─────────────────────────────────────────────────────────────────

// wt_drain — coalesce every staged delta into ONE load-merge against the owner.
//
// Returns: nodes_added on success (>= 0), 0 when there was nothing to do, and
// -1 when the push FAILED. -1 is load-bearing: on failure the spool files are
// left untouched, so nothing is lost and the next drain retries them. A caller
// must never read a non-negative return as "my particular node is durable" —
// use wt_durable(id) for that.
//
// Concurrency: several threads may drain at once. Each builds its own batch file
// (uuid-named), and overlapping batches are harmless because load-merge dedups.
// Files are truncated ONLY after a confirmed ok:true, so a lost race costs a
// redundant push, never a dropped write.
fn wt_drain() -> Int {
    if !wt_enabled() { return 0 }
    let dir: String = wt_spool_dir()
    if str_eq(dir, "") { return 0 }

    // el_list_len/el_list_get, NOT json_stringify(fs_list(...)): fs_list builds
    // a native list via el_list_append, and json_stringify does not serialize
    // that type — it renders the raw pointer value. (Verified in isolation; the
    // same latent defect is live in studio.el's /api/tools/file/list route,
    // which returns e.g. {"entries":4386409744}. Noted, not fixed here.)
    let listing = fs_list(dir)
    let count: Int = el_list_len(listing)
    if count == 0 { return 0 }

    let nodes_acc: String = ""
    let edges_acc: String = ""
    let drained: String = ""
    let found: Int = 0
    let i: Int = 0
    // No `continue` / `break`: elc lists them as keywords but not one line of
    // the shipped soul uses either, so they are unexercised on this build path.
    // Guard conditions are expressed as nested ifs instead, and every rebind is
    // at the loop-body top level where `let x = ...` is assignment (the idiom
    // memory.el's boot-counter loop relies on) — never inside a nested block,
    // where it would shadow instead.
    while i < count {
        let name: String = el_list_get(listing, i)
        // A delta is only usable when it ends with the closing "]}" that
        // wt_stage writes last. fs_write is not atomic, so a file being written
        // right now can be observed half-formed; requiring the terminator means
        // it is picked up whole on the next drain instead of merged as garbage.
        // An empty read means "already drained and truncated" — not an error.
        let p: String = if str_starts_with(name, "wt-") { dir + "/" + name } else { "" }
        let raw: String = if str_eq(p, "") { "" } else { wt_read(p) }
        let usable: Bool = !str_eq(raw, "") && str_ends_with(raw, "]}")
        let nj: String = if usable { wt_inner(json_get_raw(raw, "nodes")) } else { "" }
        let ej: String = if usable { wt_inner(json_get_raw(raw, "edges")) } else { "" }
        let nodes_acc = if str_eq(nj, "") { nodes_acc } else if str_eq(nodes_acc, "") { nj } else { nodes_acc + "," + nj }
        let edges_acc = if str_eq(ej, "") { edges_acc } else if str_eq(edges_acc, "") { ej } else { edges_acc + "," + ej }
        let drained = if !usable { drained } else if str_eq(drained, "") { p } else { drained + "\n" + p }
        let found = if usable { found + 1 } else { found }
        let i = i + 1
    }

    if found == 0 { return 0 }

    let combined: String = "{\"nodes\":[" + nodes_acc + "],\"edges\":[" + edges_acc + "]}"
    let batch: String = dir + "/wtb-" + uuid_v4() + ".json"
    fs_write(batch, combined)
    if str_eq(wt_read(batch), "") {
        println("[persist] wt_drain: could not write batch file " + batch + " — " + int_to_str(found) + " deltas stay queued")
        return -1
    }

    let url: String = wt_engram_url()
    let key: String = wt_api_key()
    let body: String = "{\"path\":\"" + wt_esc(batch) + "\",\"_auth\":\"" + wt_esc(key) + "\"}"
    let resp: String = http_post_json(url + "/api/load-merge", body)

    // The batch file is pure scratch — the retry is rebuilt from the SPOOL, not
    // from it. Truncate it unconditionally, before branching on the outcome, so
    // a persistently unreachable owner cannot accumulate one husk per attempt.
    fs_write(batch, "")

    // Distinguish the two failures rather than collapsing them: "cannot reach
    // the owner" and "the owner refused this delta" need different human
    // responses, and a log line that says the wrong one costs a debugging hour.
    // curl surfaces transport errors as a JSON body, so an empty response is not
    // the only unreachable signal.
    // (str_contains rather than a strict parse on purpose — the engram's HTTP
    //  responses have been observed carrying trailing bytes past the JSON.)
    let unreachable: Bool = str_eq(resp, "")
        || str_contains(resp, "Couldn't connect")
        || str_contains(resp, "Failed to connect")
        || str_contains(resp, "Could not resolve")
        || str_contains(resp, "timed out")
    if unreachable {
        wt_sweep(dir)
        println("[persist] wt_drain: owner UNREACHABLE at " + url + " — " + int_to_str(found)
            + " deltas stay queued in " + dir + " (will retry): " + resp)
        return -1
    }
    if !str_contains(resp, "\"ok\":true") {
        wt_sweep(dir)
        println("[persist] wt_drain: owner REJECTED the delta — " + int_to_str(found)
            + " stay queued in " + dir + ": " + resp)
        return -1
    }

    let added: Int = json_get_int(resp, "nodes_added")
    let added_e: Int = json_get_int(resp, "edges_added")

    // Confirmed. Truncate the drained spool files so they are not re-pushed.
    // Truncation (not deletion) because the runtime exposes no unlink builtin;
    // an emptied file is inert to the loop above. The zero-byte husks are then
    // swept below.
    let paths = str_split(drained, "\n")
    let pn: Int = el_list_len(paths)
    let k: Int = 0
    while k < pn {
        let one: String = el_list_get(paths, k)
        if !str_eq(one, "") { fs_write(one, "") }
        let k = k + 1
    }
    wt_sweep(dir)

    println("[persist] wt_drain: pushed " + int_to_str(found) + " deltas -> owner added "
        + int_to_str(added) + " nodes, " + int_to_str(added_e) + " edges")
    return added
}

// wt_durable — is this id present AT THE OWNER? The only honest answer to
// "did my write persist" in HTTP mode.
//
// In file mode the soul IS the owner, so the local read-back is the owner-side
// read-back and this collapses to the pre-existing check.
//
// nodes_added from wt_drain is NOT a substitute: a concurrent drain may have
// already pushed this node, making our own added count 0 while the node is
// perfectly durable. Presence at the owner is the fact; counts are telemetry.
fn wt_durable(id: String) -> Bool {
    if str_eq(id, "") { return false }
    if !wt_enabled() {
        let local: String = engram_get_node_json(id)
        return !str_eq(local, "") && !str_eq(local, "null") && !str_eq(local, "{}")
    }
    let url: String = wt_engram_url()
    let resp: String = http_get(url + "/api/nodes/" + id)
    if str_eq(resp, "") { return false }
    if str_eq(resp, "{}") { return false }
    return str_contains(resp, "\"id\"")
}

// wt_commit — flush, then assert at the owner. The receipt callers should use.
// Deliberately NOT a fixed success shape: it can and does return false while the
// local write is perfectly fine in RAM, which is the true state of affairs when
// the owner is unreachable.
fn wt_commit(id: String) -> Bool {
    if str_eq(id, "") { return false }
    if !wt_enabled() {
        let local: String = engram_get_node_json(id)
        return !str_eq(local, "") && !str_eq(local, "null") && !str_eq(local, "{}")
    }
    let pushed: Int = wt_drain()
    return wt_durable(id)
}