feat(diagnostics): the issue composer — draft, review, screenshots, zip export (E16 S3)

After Stop (or at the cap, or from Settings → Diagnosztika's past sessions)
one dialog drafts the issue: title, description, the steps drafted from the
session's markers and page changes (a marker without a label is named by its
time), the environment (version, browser, system, window, language). Beside
it, what goes with it: the browser and server logs — each reviewable line by
line, an unticked line is not sent — and the screenshots, removable, with
paste / drop / pick to add more.

- it saves as it goes (debug_sessions.draft, migration 0090): the rendered
  markdown in the user's language, the excluded rows, and its own fields to
  reopen as it was; a sent session is read-only
- the zip export (issue.md, client.log, server.log, screenshots) is built
  from the saved draft by app/issues/bundle.py — the one definition the Gitea
  delivery (S4) will share; .log, not .jsonl, which Gitea refuses
- the log line's level tags and clock move to components/logLineParts so the
  review list draws a level the way both log viewers do

backend/app/routes/debug_sessions.py

@@ -10,10 +10,12 @@ form — one image per request, capped while it arrives, and kept only if its by
 those types, whatever the Content-Type claimed.
 """
 
+import json
 from datetime import datetime, timezone
+from typing import Any
 
 from fastapi import APIRouter, Depends, HTTPException, Request, Response
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from sqlalchemy import select
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
@@ -21,6 +23,7 @@ from sqlalchemy.orm import Session
 from app import debugsession, logs, logsink
 from app.auth import require_human
 from app.db import get_db
+from app.issues import bundle
 from app.models import DebugScreenshot, DebugSession, User
 from app.routes._common import capped_body, not_found, owned_or_404
 from app.utils import iso
@@ -111,6 +114,59 @@ def session_events(
     return {"items": [logsink.serialize(r) for r in rows], "total": total}
 
 
+# --- the draft and its export ---------------------------------------------------------------
+# The composer's own fields (steps, description…) are its business, kept whole so it reopens as it
+# was — bounded here so a draft cannot become a place to store anything else.
+FORM_MAX_BYTES = 64 * 1024
+
+
+class DraftIn(BaseModel):
+    title: str = Field(max_length=200)
+    # The rendered markdown the export and the issue carry.
+    body: str = Field(max_length=50_000)
+    # Log rows taken out of the evidence in the review.
+    excluded: list[int] = Field(default_factory=list, max_length=debugsession.BUNDLE_MAX)
+    form: dict[str, Any] = Field(default_factory=dict)
+
+
+@router.put("/{sid}/draft")
+def save_draft(
+    sid: str,
+    body: DraftIn,
+    user: User = Depends(require_human),
+    db: Session = Depends(get_db),
+) -> dict:
+    session = owned_or_404(db, DebugSession, sid, user, what="debug_session")
+    if session.issue_url is not None:
+        # Sent: the issue is on the tracker now, and a draft edited after it would say otherwise.
+        raise HTTPException(status_code=409, detail={"code": "already_sent"})
+    if len(json.dumps(body.form, ensure_ascii=False).encode()) > FORM_MAX_BYTES:
+        raise HTTPException(status_code=413, detail={"code": "too_large"})
+    debugsession.save_draft(session, body.model_dump())
+    db.commit()
+    return {"ok": True, "session": _view(db, session)}
+
+
+@router.get("/{sid}/export")
+def export_session(
+    sid: str, user: User = Depends(require_human), db: Session = Depends(get_db)
+) -> Response:
+    """The issue as a zip — the text, the two logs and the screenshots — for an instance without an
+    issue tracker, or for sending it by hand. Built from the SAVED draft: what the composer shows is
+    what it saved."""
+    session = owned_or_404(db, DebugSession, sid, user, what="debug_session")
+    data = bundle.zipped(bundle.files(db, session))
+    name = f"siftlode-debug-{session.started_at:%Y%m%d-%H%M}-{session.id[:6]}.zip"
+    return Response(
+        content=data,
+        media_type="application/zip",
+        headers={
+            "Content-Disposition": f'attachment; filename="{name}"',
+            "Cache-Control": "no-store",
+        },
+    )
+
+
 # --- screenshots ---------------------------------------------------------------------------
 def _shot_view(shot: DebugScreenshot) -> dict:
     return {"id": shot.id, "mime": shot.mime, "size": shot.size, "created_at": iso(shot.created_at)}