feat: initial import — SVN↔Git bi-directional mirror for Gitea

Server-side sidecar daemon. Uses own SQLite mapping table (not git svn)
so Git commit hashes never change. Pure Python, zero framework deps.

Includes:
- SVN→Git sync engine with nested-directory tree reconstruction
- Git→SVN push with author mapping and working-copy management
- Branch/tag sync (svn copy → git branch/tag and reverse)
- Gitea integration (on-disk push/fetch, webhook receiver)
- Reconciliation tool for divergence recovery (assess + auto-fix)
- Full end-to-end regression test (bash, 34 checks)
- systemd unit and deployment docs

Only external dependency: PyYAML (config parsing).

svn_mirror/gitea.py

@@ -0,0 +1,138 @@
+"""Gitea integration – push/pull between canonical repo and Gitea's on-disk repo."""
+
+import logging
+import os
+import subprocess
+from pathlib import Path
+from typing import Optional
+
+from .mirror import Mirror
+
+logger = logging.getLogger(__name__)
+
+
+class GiteaError(Exception):
+    pass
+
+
+def _get_gitea_repo_path(mirror: Mirror) -> Path:
+    """Return the filesystem path to Gitea's bare repo for this mirror."""
+    try:
+        return Path(mirror.config.gitea.repo_dir)
+    except Exception as e:
+        raise GiteaError(str(e))
+
+
+# ─── Git subprocess helper ─────────────────────────────────────
+
+
+def _git(*args: str, timeout: int = 300, check: bool = True) -> str:
+    """Run a git command (uses CWD for repo discovery)."""
+    try:
+        r = subprocess.run(
+            ["git"] + list(args),
+            capture_output=True,
+            text=True,
+            timeout=timeout,
+            env={**os.environ, "LC_ALL": "C"},
+        )
+    except FileNotFoundError:
+        raise GiteaError("git not found on PATH")
+    except subprocess.TimeoutExpired:
+        raise GiteaError(f"git timed out: {' '.join(args)}")
+    if check and r.returncode != 0:
+        raise GiteaError(
+            f"git failed (exit {r.returncode}): "
+            f"git {' '.join(args)}\n{r.stderr.strip()}"
+        )
+    return r.stdout.strip() if r.returncode == 0 else ""
+
+
+# ─── Push canonical → Gitea ───────────────────────────────────
+
+
+def push_to_gitea(mirror: Mirror) -> bool:
+    """Push all heads and tags from the canonical repo to Gitea's bare repo.
+
+    Returns True if anything was pushed.
+    """
+    gitea_path = _get_gitea_repo_path(mirror)
+    if not gitea_path.exists():
+        logger.warning("Gitea repo not found at %s – skipping push", gitea_path)
+        return False
+
+    canonical = str(mirror.canonical_dir)
+
+    # Check if there's anything to push by comparing refs
+    out = _git("--git-dir", canonical, "for-each-ref",
+               "--format=%(objectname) %(refname)",
+               "refs/heads/", "refs/tags/",
+               timeout=30, check=False)
+    if out:
+        has_new = False
+        for line in out.splitlines():
+            line = line.strip()
+            if not line:
+                continue
+            obj_hash, ref = line.split(None, 1)
+            gitea_hash = _git("--git-dir", str(gitea_path), "rev-parse",
+                              "--verify", "--quiet", ref,
+                              timeout=30, check=False)
+            if obj_hash != gitea_hash:
+                has_new = True
+                break
+        if not has_new:
+            logger.debug("No new commits to push to Gitea")
+            return False
+
+    logger.info("Pushing canonical → Gitea (%s) …", gitea_path)
+    # Use `git push --prune` with explicit refspecs to mirror branches and tags
+    _git(
+        "--git-dir", canonical, "push", "--prune",
+        str(gitea_path),
+        "+refs/heads/*:refs/heads/*",
+        "+refs/tags/*:refs/tags/*",
+        timeout=300,
+    )
+    logger.info("Push to Gitea complete")
+    return True
+
+
+# ─── Fetch Gitea → canonical ──────────────────────────────────
+
+
+def fetch_from_gitea(mirror: Mirror, ref: Optional[str] = None) -> bool:
+    """Fetch refs from Gitea's bare repo into the canonical repo.
+
+    If *ref* is given (e.g. ``refs/heads/master``), only that ref is
+    fetched.  Otherwise all heads are fetched.
+
+    Returns True if anything new was fetched.
+    """
+    gitea_path = _get_gitea_repo_path(mirror)
+    if not gitea_path.exists():
+        raise GiteaError(f"Gitea repo not found at {gitea_path}")
+
+    canonical = str(mirror.canonical_dir)
+
+    if ref:
+        refspec = f"+{ref}:{ref}"
+    else:
+        refspec = "+refs/heads/*:refs/heads/*"
+
+    logger.info("Fetching %s → canonical …", gitea_path)
+    _git(
+        "--git-dir", canonical, "fetch", "--prune",
+        str(gitea_path), refspec,
+        timeout=300,
+    )
+
+    # Check if anything changed
+    out = _git("--git-dir", canonical, "rev-list", "--count",
+               f"HEAD..FETCH_HEAD", timeout=30, check=False)
+    if out and out.strip() != "0":
+        logger.info("Fetched new commits from Gitea")
+        return True
+
+    logger.debug("No new commits from Gitea")
+    return False