diff --git a/lua/git/cmd.lua b/lua/git/cmd.lua
index 4fc9caa..302c64a 100644
--- a/lua/git/cmd.lua
+++ b/lua/git/cmd.lua
@@ -7,90 +7,13 @@ local M = {}
 
 ---@class ow.Git.Cmd.SplitHandler
 ---@field ft string
----@field needs_rev boolean?
----@field on_state? fun(state: ow.Git.Repo.BufState, r: ow.Git.Repo, args: string[])
-
----@param r ow.Git.Repo
----@param args string[]  -- diff args including leading "diff"
----@return string left_ref
----@return string? right_ref  -- nil means worktree
-local function compute_diff_refs(r, args)
-    local cached = false
-    local positional = {} ---@type string[]
-    local saw_separator = false
-    for i = 2, #args do
-        local a = args[i]
-        if saw_separator then
-            break
-        elseif a == "--" then
-            saw_separator = true
-        elseif a == "--cached" or a == "--staged" then
-            cached = true
-        elseif a:sub(1, 1) ~= "-" then
-            table.insert(positional, a)
-        end
-    end
-
-    local function defaults()
-        if cached then
-            return "HEAD", ":"
-        end
-        return ":", nil
-    end
-
-    if #positional == 0 then
-        return defaults()
-    end
-
-    local first = positional[1] --[[@as string]]
-    if #positional == 1 then
-        local lhs, rhs = first:match("^(.-)%.%.%.(.+)$")
-        if lhs then
-            return (lhs ~= "" and lhs or "HEAD"), rhs
-        end
-        lhs, rhs = first:match("^(.-)%.%.(.+)$")
-        if lhs then
-            return (lhs ~= "" and lhs or "HEAD"),
-                (rhs ~= "" and rhs or "HEAD")
-        end
-        if r:rev_parse(first, true) then
-            if cached then
-                return first, ":"
-            end
-            return first, nil
-        end
-        return defaults()
-    end
-
-    local second = positional[2] --[[@as string]]
-    local first_ok = r:rev_parse(first, true) ~= nil
-    if first_ok and r:rev_parse(second, true) then
-        return first, second
-    end
-    if first_ok then
-        if cached then
-            return first, ":"
-        end
-        return first, nil
-    end
-    return defaults()
-end
 
 ---@type table<string, ow.Git.Cmd.SplitHandler>
 local SPLIT_HANDLERS = {
     log = { ft = "git" },
-    diff = {
-        ft = "gitdiff",
-        on_state = function(state, r, args)
-            local left, right = compute_diff_refs(r, args)
-            state.left_ref = left
-            state.right_ref = right
-        end,
-    },
+    diff = { ft = "git" },
 }
 
-M._compute_diff_refs = compute_diff_refs
-
 ---@type string[]?
 local cached_cmds
 
@@ -207,28 +130,16 @@ function M.parse_args(line)
     return args
 end
 
----@param args string[]
----@param start integer
----@return string?
-local function first_positional(args, start)
-    for i = start, #args do
-        local a = args[i]
-        if a:sub(1, 1) ~= "-" then
-            return a
-        end
-    end
-end
-
 ---@param name string
 ---@return integer buf
 local function place_split(name)
-    local buf = vim.fn.bufnr("\\V" .. name)
-    if buf == -1 then
-        buf = util.new_scratch({ name = name, bufhidden = "hide" })
-        return buf
-    end
+    -- bufadd resolves the name the same way nvim_buf_set_name does
+    -- (cwd-prefixing for non-absolute names), so calling it twice with
+    -- the same name returns the same buffer.
+    local buf = vim.fn.bufadd(name)
     if not vim.api.nvim_buf_is_loaded(buf) then
         vim.fn.bufload(buf)
+        util.setup_scratch(buf, { bufhidden = "hide" })
     end
     local win = vim.fn.bufwinid(buf)
     if win ~= -1 then
@@ -278,9 +189,7 @@ end
 ---@param args string[]
 ---@param conf ow.Git.Cmd.SplitHandler
 local function run_in_split(r, args, conf)
-    local cmd = { "git" }
-    vim.list_extend(cmd, args)
-    util.exec(cmd, {
+    util.git(args, {
         cwd = r.worktree,
         on_done = function(stdout)
             if not stdout then
@@ -291,19 +200,6 @@ local function run_in_split(r, args, conf)
             object.attach_dispatch(buf)
             attach_history_keys(buf)
             local state = r:state(buf) --[[@as -nil]]
-            state.sha = nil
-            state.parent_sha = nil
-            if conf.needs_rev then
-                local user_rev = first_positional(args, 2) or "HEAD"
-                local sha = r:rev_parse(user_rev, true)
-                if sha then
-                    state.sha = sha
-                    state.parent_sha = r:rev_parse(user_rev .. "^", true)
-                end
-            end
-            if conf.on_state then
-                conf.on_state(state, r, args)
-            end
             vim.bo[buf].filetype = conf.ft
             -- Force a new undo block so each rerun is its own undo step.
             vim.bo[buf].undolevels = vim.bo[buf].undolevels
@@ -386,7 +282,7 @@ function M.run(args)
             object.open(r, args[2])
             return
         end
-        run_in_split(r, args, { ft = "git", needs_rev = true })
+        run_in_split(r, args, { ft = "git" })
         return
     end
 
@@ -395,7 +291,7 @@ function M.run(args)
             object.open(r, args[3])
             return
         end
-        run_in_split(r, args, { ft = "git", needs_rev = true })
+        run_in_split(r, args, { ft = "git" })
         return
     end
 
diff --git a/lua/git/commit.lua b/lua/git/commit.lua
index 2b29cfd..584ff48 100644
--- a/lua/git/commit.lua
+++ b/lua/git/commit.lua
@@ -28,11 +28,13 @@ function M.commit(opts)
             f:close()
         end
 
-        local buf, win = util.new_scratch({ name = file_path })
+        local buf, win = util.new_scratch({
+            name = file_path,
+            buftype = "acwrite",
+            modifiable = true,
+        })
         proxy_buf = buf
         proxy_win = win
-        vim.bo[buf].buftype = "acwrite"
-        vim.bo[buf].modifiable = true
         vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)
         vim.bo[buf].modified = false
         vim.bo[buf].filetype = "gitcommit"
diff --git a/lua/git/log_view.lua b/lua/git/log_view.lua
index 322fa9d..2ee59f2 100644
--- a/lua/git/log_view.lua
+++ b/lua/git/log_view.lua
@@ -97,10 +97,7 @@ function M.read_uri(buf)
     end
     repo.bind(buf, r)
 
-    vim.bo[buf].swapfile = false
-    vim.bo[buf].bufhidden = "delete"
-    vim.bo[buf].buftype = "nofile"
-    vim.bo[buf].modifiable = false
+    util.setup_scratch(buf, { bufhidden = "delete" })
     if vim.bo[buf].filetype ~= "gitlog" then
         vim.bo[buf].filetype = "gitlog"
     end
diff --git a/lua/git/object.lua b/lua/git/object.lua
index c2255d5..6a5068e 100644
--- a/lua/git/object.lua
+++ b/lua/git/object.lua
@@ -182,8 +182,7 @@ local function populate(buf, r, rev, state, rev_sha)
     if rev.path == nil then
         local commit_sha = r:rev_parse(rev_str .. "^{commit}", true)
         if commit_sha then
-            local patch = util.exec({
-                "git",
+            local patch = util.git({
                 "diff-tree",
                 "-p",
                 "-m",
@@ -195,7 +194,6 @@ local function populate(buf, r, rev, state, rev_sha)
             if patch then
                 stdout = (stdout:gsub("\n*$", "\n\n")) .. patch
             end
-            state.parent_sha = r:rev_parse(commit_sha .. "^", true)
         end
     end
 
@@ -220,8 +218,12 @@ function M.read_uri(buf)
     repo.bind(buf, r)
     local state = r:state(buf) --[[@as -nil]]
 
-    vim.bo[buf].swapfile = false
-    vim.bo[buf].bufhidden = "delete"
+    local writable = rev.stage == 0 and rev.path ~= nil
+    util.setup_scratch(buf, {
+        bufhidden = "delete",
+        buftype = writable and "acwrite" or "nofile",
+        modifiable = writable,
+    })
 
     local rev_sha = r:rev_parse(rev:format(), true)
     if not rev_sha then
@@ -234,15 +236,9 @@ function M.read_uri(buf)
 
     state.immutable = is_immutable_rev(rev)
 
-    if rev.stage == 0 and rev.path then
-        vim.bo[buf].buftype = "acwrite"
-        if not state.index_writer then
-            attach_index_writer(buf, r, rev.path)
-            state.index_writer = true
-        end
-    else
-        vim.bo[buf].buftype = "nofile"
-        vim.bo[buf].modifiable = false
+    if writable and not state.index_writer then
+        attach_index_writer(buf, r, rev.path --[[@as string]])
+        state.index_writer = true
     end
 
     if rev.path then
@@ -283,35 +279,47 @@ local function refresh(buf, r)
     end
 end
 
----@param r ow.Git.Repo
----@param ref string?  -- nil = worktree, ":" = index, else commit/sha
+---@param buf integer
+---@param path string
+local function set_ft_from_path(buf, path)
+    local ft = vim.filetype.match({ filename = path, buf = buf })
+    if ft then
+        vim.bo[buf].filetype = ft
+    end
+end
+
+---@param r ow.Git.Repo
+---@param blob string?
 ---@param path string
----@param blob string?  -- diff section blob hash; if zero, side has no content
 ---@return integer?
-local function side_buf(r, ref, path, blob)
-    if blob and is_zero(blob) then
+local function side_buf(r, blob, path)
+    if not blob or is_zero(blob) then
         return nil
     end
-    if ref == nil then
-        local p = vim.fs.joinpath(r.worktree, path)
-        if not vim.uv.fs_stat(p) then
-            return nil
-        end
+    local full, status = r:resolve_sha(blob)
+    if status == "ambiguous" then
+        util.error("ambiguous blob abbreviation: %s", blob)
+        return nil
+    end
+    if full then
+        local buf = M.buf_for(r, Revision.new({ base = full }))
+        set_ft_from_path(buf, path)
+        return buf
+    end
+    local p = vim.fs.joinpath(r.worktree, path)
+    if vim.uv.fs_stat(p) then
         local buf = vim.fn.bufadd(p)
         vim.fn.bufload(buf)
         return buf
     end
-    local rev = ref == ":" and Revision.new({ stage = 0, path = path })
-        or Revision.new({ base = ref, path = path })
-    return M.buf_for(r, rev)
+    return nil
 end
 
 ---@param r ow.Git.Repo
----@param ref string?
----@param path string
 ---@param blob string?
-local function load_side(r, ref, path, blob)
-    local buf = side_buf(r, ref, path, blob)
+---@param path string
+local function load_side(r, blob, path)
+    local buf = side_buf(r, blob, path)
     if not buf then
         util.error("no content for %s", path)
         return
@@ -321,16 +329,14 @@ local function load_side(r, ref, path, blob)
 end
 
 ---@param r ow.Git.Repo
----@param left_ref string?
----@param right_ref string?
 ---@param section ow.Git.DiffSection
-local function open_section(r, left_ref, right_ref, section)
+local function open_section(r, section)
     if not section.blob_a or not section.blob_b then
         util.error("no index line, cannot determine blob SHAs")
         return
     end
-    local left = side_buf(r, left_ref, section.path_a, section.blob_a)
-    local right = side_buf(r, right_ref, section.path_b, section.blob_b)
+    local left = side_buf(r, section.blob_a, section.path_a)
+    local right = side_buf(r, section.blob_b, section.path_b)
     if left and right then
         require("git.diff").open(left, right, true)
         return
@@ -377,36 +383,24 @@ function M.open_under_cursor()
     local line = vim.api.nvim_get_current_line()
     local r = s.repo
 
-    if s.sha and not s.left_ref then
-        local sha = line:match("^commit (%x+)$")
-            or line:match("^parent (%x+)$")
-            or line:match("^tree (%x+)$")
-            or line:match("^object (%x+)$")
-        if sha then
-            M.open(r, sha, { split = false })
-            return true
-        end
-
-        local entry_type, entry_sha, entry_name =
-            line:match("^%d+ (%w+) (%x+)\t(.+)$")
-        if entry_sha then
-            local nav_rev = entry_type == "blob"
-                    and Revision.new({ base = s.sha, path = entry_name }):format()
-                or entry_sha
-            M.open(r, nav_rev, { split = false })
-            return true
-        end
+    local sha = line:match("^commit (%x+)$")
+        or line:match("^parent (%x+)$")
+        or line:match("^tree (%x+)$")
+        or line:match("^object (%x+)$")
+    if sha then
+        M.open(r, sha, { split = false })
+        return true
     end
 
-    local left_ref, right_ref
-    if s.left_ref then
-        left_ref = s.left_ref
-        right_ref = s.right_ref
-    elseif s.sha then
-        left_ref = s.parent_sha or "0"
-        right_ref = s.sha
-    else
-        return false
+    local entry_type, entry_sha, entry_name =
+        line:match("^%d+ (%w+) (%x+)\t(.+)$")
+    if entry_sha then
+        if entry_type == "blob" then
+            load_side(r, entry_sha, entry_name --[[@as string]])
+        else
+            M.open(r, entry_sha, { split = false })
+        end
+        return true
     end
 
     local section = diff_section()
@@ -415,23 +409,23 @@ function M.open_under_cursor()
     end
 
     if line:match("^diff %-%-git ") then
-        open_section(r, left_ref, right_ref, section)
+        open_section(r, section)
         return true
     end
     if line:match("^%-%-%- ") then
-        load_side(r, left_ref, section.path_a, section.blob_a)
+        load_side(r, section.blob_a, section.path_a)
         return true
     end
     if line:match("^%+%+%+ ") then
-        load_side(r, right_ref, section.path_b, section.blob_b)
+        load_side(r, section.blob_b, section.path_b)
         return true
     end
     local prefix = line:sub(1, 1)
     if prefix == "+" then
-        load_side(r, right_ref, section.path_b, section.blob_b)
+        load_side(r, section.blob_b, section.path_b)
         return true
     elseif prefix == "-" then
-        load_side(r, left_ref, section.path_a, section.blob_a)
+        load_side(r, section.blob_a, section.path_a)
         return true
     end
     return false
diff --git a/lua/git/repo.lua b/lua/git/repo.lua
index 7b3adfd..b6140e7 100644
--- a/lua/git/repo.lua
+++ b/lua/git/repo.lua
@@ -15,9 +15,6 @@ end
 ---@class ow.Git.Repo.BufState
 ---@field repo ow.Git.Repo
 ---@field sha string?
----@field parent_sha string?
----@field left_ref string?
----@field right_ref string?
 ---@field initialized boolean?
 ---@field immutable boolean?
 ---@field index_writer boolean?
@@ -318,6 +315,30 @@ function Repo:rev_parse(rev, short)
     return trimmed ~= "" and trimmed or nil
 end
 
+---@alias ow.Git.Repo.ResolveStatus "ok"|"ambiguous"|"missing"
+
+---@param prefix string
+---@return string? full_sha
+---@return ow.Git.Repo.ResolveStatus
+function Repo:resolve_sha(prefix)
+    local result = self:get_cached("resolve:" .. prefix, function(self)
+        local out = util.exec(
+            { "git", "rev-parse", "--disambiguate=" .. prefix },
+            { cwd = self.worktree, silent = true }
+        )
+        local trimmed = out and vim.trim(out) or ""
+        if trimmed == "" then
+            return { nil, "missing" }
+        end
+        local lines = util.split_lines(trimmed)
+        if #lines == 1 then
+            return { lines[1], "ok" }
+        end
+        return { nil, "ambiguous" }
+    end)
+    return result[1], result[2]
+end
+
 ---@type table<string, ow.Git.Repo> keyed by worktree
 local repos = {}
 
diff --git a/lua/git/status_view.lua b/lua/git/status_view.lua
index 4638708..a1ad66c 100644
--- a/lua/git/status_view.lua
+++ b/lua/git/status_view.lua
@@ -754,10 +754,7 @@ function M.read_uri(buf)
     end
     repo.bind(buf, r)
 
-    vim.bo[buf].buftype = "nofile"
-    vim.bo[buf].swapfile = false
-    vim.bo[buf].modifiable = false
-    vim.bo[buf].bufhidden = "hide"
+    util.setup_scratch(buf, { bufhidden = "hide" })
     vim.bo[buf].filetype = "gitstatus"
 
     ---@type integer?
diff --git a/lua/git/util.lua b/lua/git/util.lua
index c0b3f6f..02888b6 100644
--- a/lua/git/util.lua
+++ b/lua/git/util.lua
@@ -2,16 +2,19 @@ local M = {}
 
 ---@class ow.Git.Util.ScratchOpts
 ---@field name string?
----@field bufhidden ("hide"|"wipe")?
+---@field bufhidden ("hide"|"wipe"|"delete")?
+---@field buftype ("nofile"|"acwrite"|"nowrite")?
+---@field modifiable boolean?
 
 ---@param buf integer
 ---@param opts ow.Git.Util.ScratchOpts
-local function setup_scratch(buf, opts)
-    vim.bo[buf].buftype = "nofile"
+function M.setup_scratch(buf, opts)
+    vim.bo[buf].buftype = opts.buftype or "nofile"
     vim.bo[buf].bufhidden = opts.bufhidden or "wipe"
     vim.bo[buf].swapfile = false
-    vim.bo[buf].modifiable = false
+    vim.bo[buf].modifiable = opts.modifiable == true
     vim.bo[buf].modified = false
+    vim.bo[buf].buflisted = false
     if opts.name then
         pcall(vim.api.nvim_buf_set_name, buf, opts.name)
     end
@@ -52,7 +55,7 @@ end
 function M.new_scratch(opts)
     opts = opts or {}
     local buf = vim.api.nvim_create_buf(false, true)
-    setup_scratch(buf, opts)
+    M.setup_scratch(buf, opts)
     return buf, M.place_buf(buf, opts.split)
 end
 
@@ -188,6 +191,15 @@ end
 ---@field silent boolean?
 ---@field on_done fun(stdout: string?)?
 
+---@param args string[]
+---@param opts ow.Git.Util.ExecOpts?
+---@return string?
+function M.git(args, opts)
+    local cmd = { "git" }
+    vim.list_extend(cmd, args)
+    return M.exec(cmd, opts)
+end
+
 ---@param cmd string[]
 ---@param opts ow.Git.Util.ExecOpts?
 ---@return string?
diff --git a/syntax/gitdiff.vim b/syntax/gitdiff.vim
deleted file mode 100644
index a23f9f3..0000000
--- a/syntax/gitdiff.vim
+++ /dev/null
@@ -1,7 +0,0 @@
-if exists("b:current_syntax")
-    finish
-endif
-
-runtime! syntax/git.vim
-
-let b:current_syntax = "gitdiff"
diff --git a/test/git/cmd_test.lua b/test/git/cmd_test.lua
index e0dc665..28efd6e 100644
--- a/test/git/cmd_test.lua
+++ b/test/git/cmd_test.lua
@@ -234,90 +234,3 @@ t.test("complete unknown subcommand falls back to tracked paths", function()
     local matches = cmd.complete("", "G nonexistent ", 14)
     eq_sorted(matches, { "a", "b" })
 end)
-
-t.test("compute_diff_refs default is index vs worktree", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff" })
-    t.eq(left, ":")
-    t.eq(right, nil)
-end)
-
-t.test("compute_diff_refs --cached is HEAD vs index", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff", "--cached" })
-    t.eq(left, "HEAD")
-    t.eq(right, ":")
-end)
-
-t.test("compute_diff_refs --staged is HEAD vs index", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff", "--staged" })
-    t.eq(left, "HEAD")
-    t.eq(right, ":")
-end)
-
-t.test("compute_diff_refs single rev is rev vs worktree", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff", "HEAD" })
-    t.eq(left, "HEAD")
-    t.eq(right, nil)
-end)
-
-t.test("compute_diff_refs single rev with --cached is rev vs index", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right =
-        cmd._compute_diff_refs(r, { "diff", "--cached", "HEAD" })
-    t.eq(left, "HEAD")
-    t.eq(right, ":")
-end)
-
-t.test("compute_diff_refs two revs", function()
-    local dir = make_repo({ a = "x" })
-    git(dir, "commit", "--allow-empty", "-m", "second")
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right =
-        cmd._compute_diff_refs(r, { "diff", "HEAD~1", "HEAD" })
-    t.eq(left, "HEAD~1")
-    t.eq(right, "HEAD")
-end)
-
-t.test("compute_diff_refs double-dot range", function()
-    local dir = make_repo({ a = "x" })
-    git(dir, "commit", "--allow-empty", "-m", "second")
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff", "HEAD~1..HEAD" })
-    t.eq(left, "HEAD~1")
-    t.eq(right, "HEAD")
-end)
-
-t.test("compute_diff_refs triple-dot range", function()
-    local dir = make_repo({ a = "x" })
-    git(dir, "commit", "--allow-empty", "-m", "second")
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right =
-        cmd._compute_diff_refs(r, { "diff", "HEAD~1...HEAD" })
-    t.eq(left, "HEAD~1")
-    t.eq(right, "HEAD")
-end)
-
-t.test("compute_diff_refs path-only falls back to defaults", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right = cmd._compute_diff_refs(r, { "diff", "a" })
-    t.eq(left, ":")
-    t.eq(right, nil)
-end)
-
-t.test("compute_diff_refs ignores args after --", function()
-    local dir = make_repo({ a = "x" })
-    local r = assert(require("git.repo").resolve(dir))
-    local left, right =
-        cmd._compute_diff_refs(r, { "diff", "--", "HEAD" })
-    t.eq(left, ":")
-    t.eq(right, nil)
-end)