feat(domain,infra,app): rotation/rétention log.jsonl + lecture paginée (LS6)

Backend uniquement (UI React repoussée à LS7) :
- domain : port ConversationArchive + structs SegmentStats/PageCursor/PageDirection/
  TurnSlice/RotationDecision/RotationThresholds, fn pures rotation_plan/clamp_page_limit
  + consts ; re-exports lib.
- infrastructure : impl ConversationArchive pour FsConversationLog (stats/rotate/page
  + helpers), archive segmentée hors chemin chaud.
- application : ReadConversationPage + DTO + ConversationArchiveProvider (conversation/paginate),
  RotateConversationLog (conversation/rotate), exports mod/lib.
- app-tauri : AppConversationArchiveProvider + wiring (state), rotation détachée dans
  launch_agent + commande read_conversation_page (commands), DTOs (dto),
  commande enregistrée (generate_handler!).
- tests (QA, verts) : conversation_log, conversation_rotate_paginate (nouveau),
  dto (module test). Pivots INV-LS6 et cohérence fold-après-rotation verts.

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

crates/app-tauri/src/dto.rs

@@ -13,8 +13,9 @@ use application::{
     ConversationTurnWorkPreview, ConversationWorkSummary, CreateProjectInput, CreateProjectOutput,
     GitGraphOutput, HealthInput, HealthReport, LayoutKind, ListProjectsOutput, LiveSessionKind,
     OpenProjectOutput, ProjectWorkState, StopLiveAgentOutput, TicketWorkSource, TicketWorkStatus,
+    TurnPage, TurnSource, TurnView,
 };
-use domain::{AgentBusyState, Project, ProjectId, TurnRole};
+use domain::{AgentBusyState, PageCursor, PageDirection, Project, ProjectId, TurnRole};
 
 /// Request DTO for the `health` command.
 #[derive(Debug, Clone, Default, Deserialize)]
@@ -2599,3 +2600,249 @@ pub fn parse_memory_slug(raw: &str) -> Result<MemorySlug, ErrorDto> {
         message: format!("invalid memory slug: {raw}"),
     })
 }
+
+// ── Conversation pagination (lot LS6) ────────────────────────────────────────
+
+/// Request DTO for `read_conversation_page` — a human, paginated transcript read.
+///
+/// `anchor` is a turn id to paginate around (omit to start from a thread end);
+/// `direction` is `"forward"` (towards newer) or `"backward"` (towards older,
+/// default — the human view opens on the latest page); `limit` is clamped by the
+/// domain to `[1, 200]` (omit/`0` ⇒ default 50).
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ReadConversationPageRequestDto {
+    /// The owning project's id.
+    pub project_id: String,
+    /// The conversation (pair) id to read.
+    pub conversation_id: String,
+    /// Optional anchor turn id; omit to start from a thread end.
+    #[serde(default)]
+    pub anchor: Option<String>,
+    /// Pagination direction (`"forward"` or `"backward"`); defaults to backward.
+    #[serde(default)]
+    pub direction: Option<String>,
+    /// Requested page size (omit/`0` ⇒ default; clamped to `[1, 200]`).
+    #[serde(default)]
+    pub limit: Option<usize>,
+}
+
+impl ReadConversationPageRequestDto {
+    /// Builds the domain [`PageCursor`] from the request (default direction backward,
+    /// an unparseable anchor degrades to `None` = a thread-end page).
+    #[must_use]
+    pub fn cursor(&self) -> PageCursor {
+        let direction = match self.direction.as_deref() {
+            Some(d) if d.eq_ignore_ascii_case("forward") => PageDirection::Forward,
+            _ => PageDirection::Backward,
+        };
+        let anchor = self
+            .anchor
+            .as_deref()
+            .and_then(|raw| uuid::Uuid::parse_str(raw).ok())
+            .map(domain::TurnId::from_uuid);
+        PageCursor { anchor, direction }
+    }
+}
+
+/// Origin of a turn in the human transcript view (mirrors [`TurnSource`]).
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase", tag = "kind")]
+pub enum TurnSourceDto {
+    /// The human operator.
+    Human,
+    /// Another agent (delegation via `idea_ask_agent`).
+    #[serde(rename_all = "camelCase")]
+    Agent {
+        /// The originating agent id.
+        agent_id: String,
+    },
+}
+
+impl From<TurnSource> for TurnSourceDto {
+    fn from(source: TurnSource) -> Self {
+        match source {
+            TurnSource::Human => Self::Human,
+            TurnSource::Agent { agent_id } => Self::Agent {
+                agent_id: agent_id.to_string(),
+            },
+        }
+    }
+}
+
+/// One turn in the human transcript — **full text, never truncated**.
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct TurnViewDto {
+    /// Stable turn id (also the pagination anchor).
+    pub id: String,
+    /// Timestamp (epoch milliseconds).
+    pub at_ms: u64,
+    /// Turn nature (prompt, response, tool activity).
+    pub role: TurnRole,
+    /// Origin (human or delegating agent).
+    pub source: TurnSourceDto,
+    /// The turn's **complete** text (not truncated).
+    pub text: String,
+    /// Character length of the text.
+    pub text_len: usize,
+}
+
+impl From<TurnView> for TurnViewDto {
+    fn from(turn: TurnView) -> Self {
+        Self {
+            id: turn.id.to_string(),
+            at_ms: turn.at_ms,
+            role: turn.role,
+            source: turn.source.into(),
+            text: turn.text,
+            text_len: turn.text_len,
+        }
+    }
+}
+
+/// A page of the human transcript, oldest-to-newest.
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct TurnPageDto {
+    /// The page's turns, oldest to newest.
+    pub turns: Vec<TurnViewDto>,
+    /// Whether more turns exist beyond the page in the travel direction.
+    pub has_more: bool,
+    /// Last turn id of the page (anchor for the next request), or `None` if empty.
+    pub next_anchor: Option<String>,
+}
+
+impl From<TurnPage> for TurnPageDto {
+    fn from(page: TurnPage) -> Self {
+        Self {
+            turns: page.turns.into_iter().map(TurnViewDto::from).collect(),
+            has_more: page.has_more,
+            next_anchor: page.next_anchor.map(|id| id.to_string()),
+        }
+    }
+}
+
+#[cfg(test)]
+mod ls6_pagination_tests {
+    //! LS6 — DTO de la lecture humaine paginée : parsing du curseur + mapping riche
+    //! `TurnPage → TurnPageDto` (texte complet non borné, source Human/Agent, `has_more`,
+    //! `next_anchor`). C'est le « round-trip d'une page » testable sans `State` Tauri.
+
+    use super::*;
+    use application::{TurnPage, TurnSource, TurnView};
+
+    fn tid(n: u128) -> domain::TurnId {
+        domain::TurnId::from_uuid(uuid::Uuid::from_u128(n))
+    }
+
+    #[test]
+    fn request_cursor_defaults_to_backward_and_parses_anchor() {
+        // Pas de direction ⇒ backward (la vue humaine ouvre sur la page la plus récente).
+        let req = ReadConversationPageRequestDto {
+            project_id: "p".into(),
+            conversation_id: "c".into(),
+            anchor: None,
+            direction: None,
+            limit: None,
+        };
+        let cur = req.cursor();
+        assert_eq!(cur.direction, PageDirection::Backward);
+        assert_eq!(cur.anchor, None);
+
+        // Forward (insensible à la casse) + ancre UUID valide.
+        let u = uuid::Uuid::from_u128(9);
+        let req = ReadConversationPageRequestDto {
+            project_id: "p".into(),
+            conversation_id: "c".into(),
+            anchor: Some(u.to_string()),
+            direction: Some("Forward".into()),
+            limit: Some(10),
+        };
+        let cur = req.cursor();
+        assert_eq!(cur.direction, PageDirection::Forward);
+        assert_eq!(cur.anchor, Some(domain::TurnId::from_uuid(u)));
+
+        // Ancre non-UUID ⇒ dégrade en None (page depuis un bout du fil), jamais d'erreur.
+        let req = ReadConversationPageRequestDto {
+            project_id: "p".into(),
+            conversation_id: "c".into(),
+            anchor: Some("not-a-uuid".into()),
+            direction: Some("backward".into()),
+            limit: None,
+        };
+        assert_eq!(req.cursor().anchor, None);
+    }
+
+    #[test]
+    fn turn_page_dto_round_trips_full_text_and_maps_sources() {
+        let big = "Z".repeat(40_000);
+        let page = TurnPage {
+            turns: vec![
+                TurnView {
+                    id: tid(1),
+                    at_ms: 1_700_000_000_000,
+                    role: TurnRole::Prompt,
+                    source: TurnSource::Human,
+                    text: big.clone(),
+                    text_len: big.chars().count(),
+                },
+                TurnView {
+                    id: tid(2),
+                    at_ms: 1_700_000_000_001,
+                    role: TurnRole::Response,
+                    source: TurnSource::Agent {
+                        agent_id: domain::AgentId::from_uuid(uuid::Uuid::from_u128(7)),
+                    },
+                    text: "réponse".to_owned(),
+                    text_len: 7,
+                },
+            ],
+            has_more: true,
+            next_anchor: Some(tid(2)),
+        };
+
+        let dto = TurnPageDto::from(page);
+        // Texte complet préservé (non borné) + text_len.
+        assert_eq!(dto.turns[0].text.chars().count(), 40_000);
+        assert_eq!(dto.turns[0].text_len, 40_000);
+        // next_anchor stringifié, has_more porté.
+        assert!(dto.has_more);
+        assert_eq!(
+            dto.next_anchor.as_deref(),
+            Some(tid(2).to_string().as_str())
+        );
+
+        // Round-trip JSON (la « page » telle qu'envoyée au front) : camelCase + source.
+        let json = serde_json::to_value(&dto).unwrap();
+        assert_eq!(json["hasMore"], serde_json::json!(true));
+        assert_eq!(json["nextAnchor"], serde_json::json!(tid(2).to_string()));
+        assert_eq!(
+            json["turns"][0]["source"]["kind"],
+            serde_json::json!("human")
+        );
+        assert_eq!(
+            json["turns"][1]["source"]["kind"],
+            serde_json::json!("agent")
+        );
+        assert_eq!(
+            json["turns"][1]["source"]["agentId"],
+            serde_json::json!(uuid::Uuid::from_u128(7).to_string())
+        );
+        // Le texte intégral survit au passage JSON.
+        assert_eq!(
+            json["turns"][0]["text"].as_str().unwrap().chars().count(),
+            40_000
+        );
+    }
+
+    #[test]
+    fn empty_turn_page_dto_has_no_next_anchor() {
+        let dto = TurnPageDto::from(TurnPage {
+            turns: Vec::new(),
+            has_more: false,
+            next_anchor: None,
+        });
+        assert!(dto.turns.is_empty() && !dto.has_more && dto.next_anchor.is_none());
+    }
+}