feat(session): spec mode — the renderer stops resolving policy and stops writing settings

C2 of design/client-architecture-split.md, and the last of the session's overreach.

`--resolved-spec <path>` hands the session everything it needs already resolved —
effective settings, the host's clipboard decision, the profile's name — and in that mode it
performs ZERO store reads. It had been re-deriving all three, which meant policy was being
evaluated inside the thing that draws pixels, and that the spawner and the child could
disagree about a file either of them might have written in between. First-party spawns
(the shells, the CLI) always pass one now.

The compat path stays for hand-run `punktfunk-session --connect` and old Decky scripts —
but it calls the SAME helper, so the two modes cannot drift; it is the identical function
invoked in-process instead of by the parent. A spec that is named but unreadable fails
loudly rather than quietly falling back: a spawner that asked for exact settings must not
get store-derived ones instead.

The match-window write-back is gone too. The callback used to load-modify-save the shared
settings file from inside the renderer — one of that file's five concurrent writers, for a
value only the parent needs. It now reports `{"window":{w,h}}` on stdout and the spawner
persists it, on a real change only. A hand-run session still persists its own window,
because nobody is listening to its stdout there and the event alone would drop the value.

Verified on .21: a spec naming a profile that doesn't exist in the catalog is honoured
(proving no lookup happened), a missing spec errors instead of falling back, and the CLI's
spec file is written and cleaned up per launch.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

clients/cli/src/main.rs

@@ -571,6 +571,8 @@ punktfunk:// link takes. Exit codes: 0 ok, 2 connect, 3 trust, 4 renderer, 5 not
                     trust_rejected,
                 } => failure = Some((msg, trust_rejected)),
                 SessionEvent::Ended(reason) => eprintln!("{reason}"),
+                // Persisted by the brain on the way past; nothing to report here.
+                SessionEvent::Window { .. } => {}
                 SessionEvent::Exited(code) => {
                     return match failure {
                         Some((msg, true)) => {

clients/linux/src/spawn.rs

@@ -78,6 +78,12 @@ pub fn spawn_session(
         wake: false,
         connect_timeout_secs: opts.connect_timeout_secs,
         tofu,
+        // The per-host clipboard decision, resolved here so the child doesn't look it up
+        // again — matched by address, the way every other per-host lookup matches.
+        clipboard: pf_client_core::trust::KnownHosts::load()
+            .hosts
+            .iter()
+            .any(|h| h.addr == req.addr && h.port == req.port && h.clipboard_sync),
     };
 
     let persist_paired = opts.persist_paired;
@@ -96,6 +102,8 @@ pub fn spawn_session(
             trust_rejected,
         } => error = Some((msg, trust_rejected)),
         SessionEvent::Ended(msg) => ended = Some(msg),
+        // The brain persists the window size; the shell has nothing to do with it.
+        SessionEvent::Window { .. } => {}
         SessionEvent::Exited(code) => {
             let _ = sender.send(AppMsg::SessionExited {
                 req: req.clone(),

clients/session/src/console.rs

@@ -183,7 +183,9 @@ pub fn run(target: Option<&str>) -> u8 {
         window_size: crate::session_main::window_size(&settings_at_start),
         // Latched at console start (like the stats tier above): toggling Match window in
         // the console's settings screen applies from the next console launch.
-        match_window: crate::session_main::match_window(&settings_at_start),
+        // The console owns its own window across every launch, and no parent is listening to
+        // its stdout, so it keeps persisting the size itself.
+        match_window: crate::session_main::match_window(&settings_at_start, true),
         render_scale: settings_at_start.render_scale,
         render_scale_max_dim: punktfunk_core::render_scale::max_dimension(&settings_at_start.codec),
     };
@@ -218,6 +220,8 @@ pub fn run(target: Option<&str>) -> u8 {
                     let mut params = session_params(
                         &settings,
                         profile.map(|p| p.name),
+                        // In-process launch: no spawner resolved a clipboard decision for us.
+                        None,
                         addr.clone(),
                         port,
                         pin,

clients/session/src/main.rs

@@ -159,6 +159,7 @@ mod session_main {
     pub(crate) fn session_params(
         settings: &trust::Settings,
         profile: Option<String>,
+        clipboard_override: Option<bool>,
         addr: String,
         port: u16,
         pin: [u8; 32],
@@ -169,14 +170,16 @@ mod session_main {
         force_software: Arc<AtomicBool>,
         vulkan: Option<pf_client_core::video::VulkanDecodeDevice>,
     ) -> SessionParams {
-        // Per-host clipboard opt-in (design/clipboard-and-file-transfer.md §5.3), resolved
-        // here rather than passed in so every caller — a direct connect and the console's
-        // own launches — honors the same stored decision. `addr` is moved into the struct
+        // Per-host clipboard opt-in (design/clipboard-and-file-transfer.md §5.3). In spec
+        // mode the spawner already resolved it; otherwise this looks it up itself, which is
+        // the last store read the compat path still owes. `addr` is moved into the struct
         // below, so read it first.
-        let clipboard = trust::KnownHosts::load()
-            .hosts
-            .iter()
-            .any(|h| h.addr == addr && h.port == port && h.clipboard_sync);
+        let clipboard = clipboard_override.unwrap_or_else(|| {
+            trust::KnownHosts::load()
+                .hosts
+                .iter()
+                .any(|h| h.addr == addr && h.port == port && h.clipboard_sync)
+        });
         // Re-apply the shell-persisted forwarded-controller pin (stable `vid:pid:name`
         // key) to OUR gamepad service — the shells' in-process services can't reach this
         // process. Applied per params-build (idempotent; browse re-launches included) so
@@ -280,14 +283,24 @@ mod session_main {
     /// debounced resize→`Reconfigure` machinery on; the callback stores each resize-end's
     /// logical window size (load-modify-save, like the console settings screen) so the
     /// next launch opens at it.
-    pub(crate) fn match_window(settings: &trust::Settings) -> Option<Box<dyn FnMut(u32, u32)>> {
+    /// The Match-window policy hook (design/midstream-resolution-resize.md D1/D2). The
+    /// callback used to load-modify-save the shared settings file from inside the renderer —
+    /// one of that file's five concurrent writers, for a value only the parent needs. It now
+    /// REPORTS the size on stdout and the spawner persists it
+    /// (design/client-architecture-split.md §5).
+    ///
+    /// `persist_locally` keeps a hand-run session remembering its own window: nobody is
+    /// listening to stdout there, so the event alone would drop the value. A spawned session
+    /// leaves the write to its parent, which is the whole point.
+    pub(crate) fn match_window(
+        settings: &trust::Settings,
+        persist_locally: bool,
+    ) -> Option<Box<dyn FnMut(u32, u32)>> {
         settings.match_window.then(|| {
-            Box::new(|w: u32, h: u32| {
-                let mut s = trust::Settings::load();
-                if (s.last_window_w, s.last_window_h) != (w, h) {
-                    s.last_window_w = w;
-                    s.last_window_h = h;
-                    s.save();
+            Box::new(move |w: u32, h: u32| {
+                println!("{{\"window\":{{\"w\":{w},\"h\":{h}}}}}");
+                if persist_locally {
+                    pf_client_core::orchestrate::persist_window_size(w, h);
                 }
             }) as Box<dyn FnMut(u32, u32)>
         })
@@ -473,12 +486,31 @@ mod session_main {
                 return EXIT_CONNECT_FAILED;
             }
         };
-        // Global defaults with this host's settings profile overlaid — the binding on the
-        // host record, or `--profile <id|name>` for a one-off (`--profile ""` forces the
-        // defaults). Resolved through the shared helper, exactly like the console's launches.
-        let (settings, profile) = trust::effective_settings(&addr, port, profile_arg().as_deref());
-        if let Some(p) = &profile {
-            tracing::info!(profile = %p.name, id = %p.id, "streaming with a settings profile");
+        // `--resolved-spec <path>`: the spawner already did the resolving, so this process
+        // performs ZERO store reads (design/client-architecture-split.md §5) — no Settings
+        // load, no known-hosts lookup, no profile resolution. Without it (a hand-run
+        // `--connect`, an old Decky script) the session resolves for itself through the SAME
+        // helper, so the two modes cannot drift.
+        let spec = arg_value("--resolved-spec").map(std::path::PathBuf::from);
+        let (settings, profile_name, clipboard_override) = match &spec {
+            Some(path) => match pf_client_core::orchestrate::ResolvedSpec::read(path) {
+                Ok(s) => {
+                    tracing::info!(path = %path.display(), "running from a resolved spec");
+                    (s.settings, s.profile, Some(s.clipboard))
+                }
+                Err(e) => {
+                    json_line("error", &format!("resolved spec: {e}"), None);
+                    return EXIT_CONNECT_FAILED;
+                }
+            },
+            None => {
+                let (settings, profile) =
+                    trust::effective_settings(&addr, port, profile_arg().as_deref());
+                (settings, profile.map(|p| p.name), None)
+            }
+        };
+        if let Some(name) = &profile_name {
+            tracing::info!(profile = %name, "streaming with a settings profile");
         }
 
         // Trust follows the GTK client's `--connect` rules: a stored (or `--fp`) pin
@@ -540,7 +572,8 @@ mod session_main {
             #[cfg(not(feature = "ui"))]
             overlay: None,
             window_size: window_size(&settings),
-            match_window: match_window(&settings),
+            // A spawned session (spec mode) reports its window; a hand-run one persists it.
+            match_window: match_window(&settings, spec.is_none()),
             render_scale: settings.render_scale,
             render_scale_max_dim: punktfunk_core::render_scale::max_dimension(&settings.codec),
         };
@@ -549,7 +582,8 @@ mod session_main {
             pf_presenter::run_session(opts, move |gamepad, native, force_software, vulkan| {
                 session_params(
                     &settings,
-                    profile.map(|p| p.name),
+                    profile_name,
+                    clipboard_override,
                     addr,
                     port,
                     pin,

crates/pf-client-core/src/orchestrate.rs

@@ -23,6 +23,7 @@
 use crate::deeplink::{DeepLink, HostResolution, Route};
 use crate::profiles::{ProfilesFile, Resolution, StreamProfile};
 use crate::trust::{effective_settings, KnownHost, KnownHosts, Settings};
+use serde::{Deserialize, Serialize};
 use std::process::{Child, Command, Stdio};
 use std::sync::{Arc, Mutex};
 
@@ -79,6 +80,10 @@ pub struct ConnectPlan {
     /// The pin came from an advert rather than the store: persist it once the session reports
     /// ready (ready proves the host really holds that identity).
     pub tofu: bool,
+    /// Share this machine's clipboard with this host — a trust decision about the HOST, so it
+    /// lives on the record rather than in a profile, and the spawner resolves it once here
+    /// instead of the renderer looking it up again.
+    pub clipboard: bool,
 }
 
 impl ConnectPlan {
@@ -101,6 +106,7 @@ impl ConnectPlan {
             settings,
             connect_timeout_secs: None,
             tofu: false,
+            clipboard: host.clipboard_sync,
         }
     }
 
@@ -140,6 +146,17 @@ impl ConnectPlan {
             settings,
             connect_timeout_secs: None,
             tofu: false,
+            clipboard: host.clipboard_sync,
+        }
+    }
+
+    /// This plan as a [`ResolvedSpec`] — what a first-party spawner hands the session so it
+    /// performs no store reads of its own.
+    pub fn spec(&self, clipboard: bool) -> ResolvedSpec {
+        ResolvedSpec {
+            settings: self.settings.clone(),
+            clipboard,
+            profile: self.profile.as_ref().map(|p| p.name.clone()),
         }
     }
 
@@ -448,6 +465,49 @@ pub enum ConnectOutcome {
 // Session spawn + the stdout contract.
 // ---------------------------------------------------------------------------------------
 
+/// Everything a session needs, resolved by the caller — the spec `--resolved-spec` carries
+/// (design/client-architecture-split.md §5).
+///
+/// The session binary is a renderer: given this, it performs ZERO store reads. Its old habit of
+/// re-deriving state (loading `Settings`, looking up the host's `clipboard_sync`, resolving the
+/// profile) meant policy was being evaluated inside the thing that draws pixels, and that the
+/// spawner and the child could disagree about a file either of them might have written since.
+///
+/// The compat path — a hand-run `punktfunk-session --connect` with no spec — still resolves for
+/// itself, but through the *same* helper (`effective_settings`), so the two modes cannot drift.
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct ResolvedSpec {
+    /// Effective settings: the global defaults with the chosen profile already applied.
+    pub settings: Settings,
+    /// Whether this host may share the clipboard — a per-host trust decision, resolved by the
+    /// spawner rather than re-looked-up here.
+    pub clipboard: bool,
+    /// The profile's name, for the stats overlay. `None` = the global defaults.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub profile: Option<String>,
+}
+
+impl ResolvedSpec {
+    /// Write the spec somewhere the child can read it, returning the path. Temp files rather
+    /// than a pipe because the session already takes a file path elsewhere and a crashed
+    /// spawner leaves something inspectable; the name carries the pid so concurrent launches
+    /// (a shell and a CLI, or two Decky invocations) never overwrite each other's spec.
+    pub fn write_temp(&self) -> std::io::Result<std::path::PathBuf> {
+        let path = std::env::temp_dir().join(format!("punktfunk-spec-{}.json", std::process::id()));
+        let json = serde_json::to_vec_pretty(self)
+            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))?;
+        std::fs::write(&path, json)?;
+        Ok(path)
+    }
+
+    /// Read a spec written by the spawner.
+    pub fn read(path: &std::path::Path) -> std::io::Result<ResolvedSpec> {
+        let text = std::fs::read_to_string(path)?;
+        serde_json::from_str(&text)
+            .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))
+    }
+}
+
 /// One event from the session child's stdout contract (`{"ready":true}`, `{"error":…}`,
 /// `{"ended":…}`, then EOF and an exit code). Parsed in one place so a shell, the console and
 /// the CLI cannot disagree about what "ready" or "trust rejected" means.
@@ -460,6 +520,13 @@ pub enum SessionEvent {
         trust_rejected: bool,
     },
     Ended(String),
+    /// The session window's logical size settled at this, under the match-window policy. The
+    /// SPAWNER persists it (design §5): a renderer that load-modify-saves the shared settings
+    /// file was one of its five concurrent writers, for a value only the parent needs.
+    Window {
+        w: u32,
+        h: u32,
+    },
     /// EOF: the child is gone. `-1` = killed by a signal.
     Exited(i32),
 }
@@ -480,9 +547,26 @@ pub fn parse_session_line(line: &str) -> Option<SessionEvent> {
     if let Some(msg) = v.get("ended").and_then(|m| m.as_str()) {
         return Some(SessionEvent::Ended(msg.to_string()));
     }
+    if let Some(win) = v.get("window") {
+        let dim = |k: &str| win.get(k).and_then(|n| n.as_u64()).map(|n| n as u32);
+        if let (Some(w), Some(h)) = (dim("w"), dim("h")) {
+            return Some(SessionEvent::Window { w, h });
+        }
+    }
     None
 }
 
+/// Persist a window size the session reported. The spawner's job now, not the renderer's — and
+/// it writes only on a real change, so a session that never resizes never touches the file.
+pub fn persist_window_size(w: u32, h: u32) {
+    let mut s = Settings::load();
+    if (s.last_window_w, s.last_window_h) != (w, h) {
+        s.last_window_w = w;
+        s.last_window_h = h;
+        s.save();
+    }
+}
+
 /// The session binary: installed next to this executable, else `$PATH` (a dev run out of
 /// `target/…` lands on the sibling).
 pub fn session_binary() -> std::path::PathBuf {
@@ -525,7 +609,23 @@ pub fn spawn_session(
     on_event: impl FnMut(SessionEvent) + Send + 'static,
 ) -> Result<CancelHandle, String> {
     let mut cmd = Command::new(session_binary());
-    cmd.args(plan.session_args())
+    let mut args = plan.session_args();
+    // Spec mode: hand the child the settings we already resolved, so it reads no stores and
+    // cannot disagree with us about a file either of us might write (design §5). A spec we
+    // fail to write is not fatal — the child's compat path resolves the same values through
+    // the same helper, which is exactly why that path was kept.
+    let spec_path = match plan.spec(plan.clipboard).write_temp() {
+        Ok(path) => {
+            args.push("--resolved-spec".into());
+            args.push(path.to_string_lossy().into_owned());
+            Some(path)
+        }
+        Err(e) => {
+            tracing::warn!(error = %e, "couldn't write the resolved spec; the session will resolve for itself");
+            None
+        }
+    };
+    cmd.args(args)
         .stdin(Stdio::null())
         .stdout(Stdio::piped())
         .stderr(Stdio::inherit()); // the session's logs interleave with the front-end's
@@ -550,9 +650,19 @@ pub fn spawn_session(
             for line in std::io::BufReader::new(stdout).lines() {
                 let Ok(line) = line else { break };
                 if let Some(ev) = parse_session_line(&line) {
+                    // The window size is the spawner's to persist — the renderer only reports
+                    // it. Front-ends still see the event; they just don't have to act on it.
+                    if let SessionEvent::Window { w, h } = ev {
+                        persist_window_size(w, h);
+                    }
                     on_event(ev);
                 }
             }
+            // The spec has done its job the moment the child has read it; a leftover temp file
+            // in %TEMP% is litter, and one per launch adds up.
+            if let Some(path) = &spec_path {
+                let _ = std::fs::remove_file(path);
+            }
             // EOF — reap (a cancel-killed child lands here too; -1 = died on a signal).
             let code = reader_slot
                 .0
@@ -675,6 +785,7 @@ mod tests {
             wake: true,
             connect_timeout_secs: None,
             tofu: false,
+            clipboard: false,
         };
         assert_eq!(
             plan.session_args(),
@@ -807,6 +918,65 @@ mod tests {
         ));
     }
 
+    /// The spec is the whole of what a session needs, and it round-trips — a field lost here
+    /// is a setting the stream silently doesn't get.
+    #[test]
+    fn resolved_spec_round_trips() {
+        let spec = ResolvedSpec {
+            settings: Settings {
+                width: 2560,
+                height: 1440,
+                bitrate_kbps: 55000,
+                codec: "av1".into(),
+                ..Default::default()
+            },
+            clipboard: true,
+            profile: Some("Work".into()),
+        };
+        let json = serde_json::to_string(&spec).unwrap();
+        assert_eq!(serde_json::from_str::<ResolvedSpec>(&json).unwrap(), spec);
+
+        // A spec without a profile is the defaults, and the key is simply absent.
+        let plain = ResolvedSpec {
+            profile: None,
+            ..spec.clone()
+        };
+        let json = serde_json::to_string(&plain).unwrap();
+        assert!(!json.contains("profile"));
+        assert_eq!(serde_json::from_str::<ResolvedSpec>(&json).unwrap(), plain);
+    }
+
+    /// A plan's spec carries the settings the plan resolved — including the profile's name for
+    /// the overlay, and the host's clipboard decision the renderer no longer looks up.
+    #[test]
+    fn plan_spec_carries_what_the_session_may_not_re_derive() {
+        let h = KnownHost {
+            name: "Desk".into(),
+            addr: "192.168.1.50".into(),
+            fp_hex: "a".repeat(64),
+            clipboard_sync: true,
+            profile_id: Some("aaaaaaaaaaaa".into()),
+            ..Default::default()
+        };
+        let catalog = ProfilesFile {
+            version: 1,
+            profiles: vec![crate::profiles::StreamProfile {
+                id: "aaaaaaaaaaaa".into(),
+                name: "Game".into(),
+                overrides: crate::profiles::SettingsOverlay {
+                    bitrate_kbps: Some(80000),
+                    ..Default::default()
+                },
+                ..crate::profiles::StreamProfile::new("")
+            }],
+        };
+        let plan = ConnectPlan::resolve(&h, None, None, &catalog, &Settings::default());
+        let spec = plan.spec(plan.clipboard);
+        assert_eq!(spec.settings.bitrate_kbps, 80000, "the overlay is baked in");
+        assert_eq!(spec.profile.as_deref(), Some("Game"));
+        assert!(spec.clipboard, "the host's decision, resolved once");
+    }
+
     /// The stdout contract, parsed once for every front-end.
     #[test]
     fn session_contract_lines() {
@@ -832,6 +1002,14 @@ mod tests {
             parse_session_line(r#"{"ended":"Host ended the session"}"#),
             Some(SessionEvent::Ended("Host ended the session".into()))
         );
+        // The window report the spawner persists on the session's behalf.
+        assert_eq!(
+            parse_session_line(r#"{"window":{"w":1600,"h":900}}"#),
+            Some(SessionEvent::Window { w: 1600, h: 900 })
+        );
+        // A half-formed window line is not an event — persisting half a size would be worse
+        // than ignoring it.
+        assert_eq!(parse_session_line(r#"{"window":{"w":1600}}"#), None);
         // Stats lines and stray output are never events.
         assert_eq!(parse_session_line("stats: 1280×800@60 · 60 fps"), None);
         assert_eq!(parse_session_line(""), None);