feat(git): 3-way merge editor, reflog, rebase/interactive rebase, reset with undo, force-with-lease push, remote branches and remotes

Server: git-rewrite.js (rebase + continue/skip/abort, rebase-interactive with
no editor, reset soft/mixed/keep/hard, undo-rewrite, force-push with lease,
remote-branch-delete, remote add/rename/remove) and git-conflicts.js
(conflict stages read + conflict-save, reflog), dispatched from runGitAction;
operationInProgress now reports a rebase and only ALLOWED_WHILE_REBASING
writes run during one. New reads: /git/conflict, /git/reflog, /git/remotes,
/git/rewrite-plan. Client: History tools menu, MergeEditor, ReflogView,
RebaseDialog, InteractiveRebase, ResetDialog, ForcePushDialog, RemotesDialog,
rebase banner Skip. CLAUDE.md git-writes rule rewritten for the new actions.

docs/API.md

@@ -1123,6 +1123,44 @@ each call spends the user's Claude quota. Answers `{"message": "..."}`;
 for a path git does not report changed, `400 ENOTOOL` without `claude` on PATH,
 `502 EAI` when the CLI fails, answers empty or runs past 120 s.
 
+#### Conflicts, reflog, remotes and rewrite plans
+
+```http
+GET /api/lanes/:id/git/conflict?path=<path>
+GET /api/lanes/:id/git/reflog?ref=HEAD|<branch>&skip=0&limit=50
+GET /api/lanes/:id/git/remotes
+GET /api/lanes/:id/git/rewrite-plan?kind=rebase&onto=<branch>
+GET /api/lanes/:id/git/rewrite-plan?kind=interactive[&base=<sha>]
+GET /api/lanes/:id/git/rewrite-plan?kind=reset&target=<sha>
+GET /api/lanes/:id/git/rewrite-plan?kind=push
+```
+
+Reads (no same-origin guard), all taking `?session=`/`?source=`/`?repo=` like
+the other git routes (`server/lib/git-conflicts.js`, `server/lib/git-rewrite.js`).
+
+- **`/git/conflict`** — the 3-way merge editor's input for a path
+  `git ls-files -u` lists as unmerged right now (else `400 EBADPATH`), with
+  `/git/file`'s guards (`403 ESECRET`, 1 MB cap): `{operation, branch,
+  incoming: {sha, short, subject}|null, base, ours, theirs, working, sha,
+  usable, binary, tooBig}`. Each side is read by its blob id (stages 1/2/3); a
+  side git does not have is `null`. `sha` is the `baseSha` `conflict-save`
+  needs. In a rebase `ours` is the branch being rebased onto and `theirs` the
+  commit being replayed.
+- **`/git/reflog`** — `git log -g` of HEAD or of a local branch that exists
+  (`400 EBADBRANCH`/`ENOBRANCH`), newest first: `{ref, more, entries:
+  [{index, selector, sha, short, action, message, time, subject}]}`.
+- **`/git/remotes`** — `{remotes: [{name, url, pushUrl, defaultBranch,
+  branches}]}`; an http(s) URL loses its whole userinfo and any other keeps only
+  the user name, so no password or token is ever answered.
+- **`/git/rewrite-plan`** — what a rewrite would do, for the dialog that asks
+  before it: every answer has `head` (the sha a write must name), `branch`,
+  `subdir`, `operation`, `dirty`; `rebase` adds `commits[]` (each with
+  `pushed`), `behind`, `pushed`; `interactive` adds `base`, `merges`,
+  `commits[]` (with full `message`), `pushed`; `reset` adds `target`,
+  `related`, `dropped`, `added`, `pushed`; `push` adds `remote`,
+  `remoteBranch`, `remoteSha` (the lease), `ahead`, `behind`, `protected`,
+  `allowed`. A bad `kind` is `400 EBADMODE`.
+
 #### Act on a workspace's working copy
 
 ```http
@@ -1166,6 +1204,16 @@ cannot collide on `index.lock`.
 | `unshelve` | `git stash apply --index <sha>` (retried without `--index` when only the index cannot be rebuilt), then `git stash drop` of that entry when it applied cleanly | `{"sha": "<shelf sha>"}` |
 | `shelf-drop` | `git stash drop` of that entry | `{"sha": "<shelf sha>", "confirm": true}` |
 | `ignore` | appends one anchored, escaped `/<path>` line per path to the WORKSPACE's own `.gitignore` (created if missing, never a line it already has) — untracked paths only (`400 ETRACKED`), never through a symlink or onto a non-regular file (`400 EBADPATH`) | `{"paths": ["..."]}` |
+| `conflict-save` | the 3-way merge editor's result written over the conflicted file through `PUT /git/file`'s guards (`baseSha` → `409 ESTALE`, `403 ESECRET`), then `git add`; a result with a marker left is `400 EMARKERS` before anything is written, unless `resolve: false` (save progress, still conflicted) | `{"path": "...", "content": "...", "baseSha": "<sha from /git/conflict>", "resolve": true}` |
+| `rebase` | `git rebase <ref>` (no editor, no autostash, no other branch moved) — a local or remote-tracking branch that exists | `{"onto": "main", "head": "<HEAD the plan showed>", "force": false}` |
+| `rebase-continue` / `rebase-skip` | `git rebase --continue` (`409 ECONFLICTS` while anything is unmerged) / `--skip` | — |
+| `rebase-abort` | `git rebase --abort` | `{"confirm": true}` |
+| `rebase-interactive` | `git rebase -i <base>` with a todo AgentHub builds from the list — no editor opens | `{"head": "<HEAD>", "base": "<sha, optional>", "todo": [{"sha": "<full sha>", "action": "pick\|reword\|squash\|fixup\|drop", "message": "..."}], "force": false, "confirm": true}` |
+| `reset` | `git reset --soft\|--mixed\|--keep\|--hard <target>` | `{"target": "<sha>", "mode": "keep", "head": "<HEAD>", "confirm": true, "force": false, "confirmBranch": "<branch, hard only>"}` |
+| `undo-rewrite` | `git reset --keep <to>` — puts the branch back where a rewrite found it | `{"to": "<before>", "head": "<after>", "confirm": true}` |
+| `force-push` | `git push -u --force-with-lease=refs/heads/<b>:<expect> <remote> HEAD:refs/heads/<b>` — `<b>` is the current branch's upstream branch | `{"expect": "<remote sha the plan showed, or \"\">", "confirm": true}` |
+| `remote-branch-delete` | `git push <remote> --delete refs/heads/<branch>` — a fetched remote-tracking branch | `{"branch": "origin/feature", "confirm": true}` |
+| `remote-add` / `remote-rename` / `remote-remove` | `git remote add -- <name> <url>` / `rename -- <name> <to>` / `remove -- <name>` | `{"name": "upstream", "url": "git@host:o/r.git"}` / `{"name": "...", "to": "..."}` / `{"name": "...", "confirm": true}` |
 
 ```json
 { "action": "commit", "ok": true, "output": "[feat/x 9b3e74a] fix: the thing" }
@@ -1184,9 +1232,8 @@ cannot collide on `index.lock`.
   changed (`400 EBADPATH`).
 - `pull` is **always** `--ff-only` and `switch` refuses a dirty tree
   (`400 EDIRTY`) unless `changes` says what happens to the changes: neither
-  can invent a merge commit or a conflict underneath a running agent. There
-  is deliberately no rebase or hard reset here — a hard `reset` stays behind
-  the destroy guard on `POST /api/lanes/:id/reset`.
+  can invent a merge commit or a conflict underneath a running agent. A
+  rebase, a reset or a force push happens only as its own action (below).
 - **Switch with changes.** `changes: "carry"` runs a plain `git switch`
   (never `--force`, `--merge` or `--discard-changes`); when git refuses
   because a carried file would be overwritten the answer is
@@ -1226,6 +1273,49 @@ cannot collide on `index.lock`.
   `switch` that carries or shelves uncommitted changes answer
   `409 EAGENTRUNNING` until resent with `confirm: true` — they move files
   under it.
+- **History rewrites** (`server/lib/git-rewrite.js`) are allowed because each
+  one's recovery is a button too. Every one runs only from a repo-root
+  workspace (`400 ESUBDIR`), never while a merge, cherry-pick, revert or rebase
+  is open (`409 EMERGING`), and names the full `head` sha the plan showed
+  (`409 ESTALE` once HEAD moved, `400 EBADSHA` without it). Rewriting a commit
+  any remote-tracking branch already holds is `409 EPUSHED` unless the body
+  says `force: true` (the UI shows that a force-push will be needed). Each
+  answers `before`/`after`; `undo-rewrite` (`reset --keep <before>`, only while
+  HEAD is still `after`) undoes it.
+  - `rebase` and `rebase-interactive` need a clean tree (`400 EDIRTY`). A stop
+    is a **200** with `conflicts[]` and `stopped: true`; while a rebase is open
+    `GET /git` reports `merging: true, operation: "rebase"`, every write except
+    `fetch`, `stage`, `unstage`, `discard`, `ignore`, `resolve`,
+    `conflict-save` and the rebase's own steps is `409 EMERGING`, and the
+    banner's `merge-commit` / `merge-abort` act as `rebase-continue` /
+    `rebase-abort` — a rebase started in a terminal included.
+    `rebase-continue`/`-skip`/`-abort` with no rebase open are `409 ENOREBASE`.
+  - `rebase-interactive`: `todo` lists EXACTLY the commits of `base..HEAD`
+    (default base: the parent of the oldest commit no remote has) by full sha,
+    each once, in the new order, else `400 EBADTODO`; a merge commit in the
+    range is `400 EMERGECOMMIT`; a list that changes nothing is
+    `400 ENOCHANGES`; a reword needs a message (`400 EBADMESSAGE`). AgentHub
+    writes the todo and the messages as 0600 files in the repo's own git dir
+    (as the folder's account), hands git `cp` as its sequence editor and `true`
+    as its editor; a squash becomes `fixup` + `exec git commit --amend -F <file>`
+    with the combined (or given) message, so no request text is ever shell.
+  - `reset`: `target` must be an ancestor or descendant of HEAD
+    (`400 ENOTRELATED`), `mode` one of soft/mixed/keep/hard (`400 EBADMODE`);
+    `hard` only on a clean tree (`400 EDIRTY`) and with `confirmBranch` equal to
+    the current branch name (`400 ECONFIRM`). `keep` refuses (git's own `409`)
+    rather than overwrite a local change.
+  - `force-push`: HEAD only, to its upstream branch, with a lease on `expect` —
+    `409 ESTALE` when the remote moved since the fetch the plan read;
+    `main`/`master`/`development`/`develop` are `400 EPROTECTED` unless the
+    server runs with `AGENTHUB_GIT_FORCE_PUSH_PROTECTED=1`; a detached HEAD is
+    `400 EDETACHED`.
+  - `remote-branch-delete` refuses a protected name (`400 EPROTECTED`) and the
+    remote's default branch (`refs/remotes/<r>/HEAD`, `400 EDEFAULTBRANCH`);
+    a branch not fetched is `400 ENOBRANCH`.
+  - `remote-add` takes its URL through `publish`'s allowlist (`400 EBADURL`)
+    and a name of letters, digits, `.`, `_`, `-` (`400 EBADREMOTE`); a taken
+    name is `400 EREMOTEEXISTS`; `remote-remove` needs `confirm: true`.
+    A stored git credential still goes only to its own host.
 - **Cherry-pick and revert** follow merge: a commit named by hex sha that
   exists (`400 EBADSHA`) and is not a merge commit (`400 EMERGECOMMIT`), a
   clean tree, a repo-root workspace. A conflict is a **200** with
@@ -1235,8 +1325,8 @@ cannot collide on `index.lock`.
   revert whose changes are already there is aborted again and answers
   `409 EEMPTY`, never left open; one git could not commit (no identity, a
   failing signer) is undone the same way and answers git's own error. A
-  rebase stopped in a terminal makes every history action, `merge-commit` and
-  `merge-abort` `409 EMERGING` — it is finished where it started.
+  rebase stopped in a terminal makes every history action `409 EMERGING`;
+  `merge-commit`/`merge-abort` then continue/abort that rebase.
 - **Undo commit and amend** rewrite the last commit, so both are
   `409 EPUSHED` once any remote-tracking branch contains HEAD, `409 ESTALE`
   when HEAD is no longer the `sha` the request names (`400 EBADSHA` without