diff --git a/MIGRATION_PLAN.md b/MIGRATION_PLAN.md
index 526ecc3..9beba66 100644
--- a/MIGRATION_PLAN.md
+++ b/MIGRATION_PLAN.md
@@ -143,10 +143,16 @@ Source of truth for the step-by-step rebuild. Keep this concise and up to date.
 - [x] Minimal UI: dropdown theme for files/buffers, no previewer for quick selection
 
 ## Phase 4.4 — Oil.nvim for file manipulation
-- [ ] Add `stevearc/oil.nvim` for filesystem operations (rename, create, delete, copy, move)
-- [ ] Configure to handle buffer name sync on file operations
-- [ ] Keep minimal - use only when shell operations would cause buffer issues
-- [ ] Note: Evaluate practicality; can switch to `mini.files` if preferred
+- [x] Add `stevearc/oil.nvim` for filesystem operations (rename, create, delete, copy, move)
+- [x] Configure to handle buffer name sync on file operations
+- [x] Keep minimal - use only when shell operations would cause buffer issues
+- [x] Keymaps configured:
+  - `<leader>fo` - Open Oil file browser (regular buffer)
+  - `<leader>fO` - Open Oil in floating window (with floating previews)
+  - `<C-p>` in Oil - Preview files (vertical split to right for regular, floating window for float mode)
+- [x] Preview splits open to the right via `vertical = true` and `split = 'belowright'`
+- [x] Floating window preview direction: `preview_split = "right"`
+- [x] Note: Evaluate practicality; can switch to `mini.files` if preferred
 
 ## Phase 5 — Treesitter
 
diff --git a/README.md b/README.md
index 9992d9d..e2885b9 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,12 @@ Record every decision here with a short rationale. Append new entries; do not re
 - 2025-12-06: Plugin approval policy — other plugins are allowed, but do not install any plugin not listed without explicit confirmation.
 - 2025-12-07: **CRITICAL REGRESSION FIX**: Neovim 0.11+ does NOT support `on_new_config` callback in `vim.lsp.config()`. Project-local settings (`.nvim.lua`) must be loaded via `LspAttach` autocmd instead. The `on_new_config` hook was silently ignored, causing empty settings and breaking goto-definition for external includes. Solution: Use `LspAttach` to load project settings, merge into `client.settings`, and send `workspace/didChangeConfiguration` notification.
 - 2025-12-07: Native `exrc` + `.nvim.lua` finalized as project-local config approach (replaces neoconf, which is incompatible with Neovim 0.11+ native LSP API). Security via `vim.opt.secure = true`.
+- 2025-12-07: Navigation Phase 4 decisions:
+  - Skip Neo-tree in favor of netrw for project visualization
+  - Use Telescope as primary "find file" tool with fuzzy finding
+  - Add Oil.nvim for file manipulation (rename/move/delete with buffer sync)
+  - netrw for tree view and preview splits; Oil for operations that would break buffer names
+  - PHP `gf` enhancement via `includeexpr` for WordPress/PHP path resolution
 
 ## Project-Local Configuration (design)
 
diff --git a/lazy-lock.json b/lazy-lock.json
index 84e3a5c..2372b87 100644
--- a/lazy-lock.json
+++ b/lazy-lock.json
@@ -8,6 +8,7 @@
   "mason.nvim": { "branch": "main", "commit": "57e5a8addb8c71fb063ee4acda466c7cf6ad2800" },
   "nvim-cmp": { "branch": "main", "commit": "d97d85e01339f01b842e6ec1502f639b080cb0fc" },
   "nvim-lspconfig": { "branch": "master", "commit": "9c923997123ff9071198ea3b594d4c1931fab169" },
+  "oil.nvim": { "branch": "master", "commit": "cbcb3f997f6f261c577b943ec94e4ef55108dd95" },
   "plenary.nvim": { "branch": "master", "commit": "b9fd5226c2f76c951fc8ed5923d85e4de065e509" },
   "telescope-fzf-native.nvim": { "branch": "main", "commit": "6fea601bd2b694c6f2ae08a6c6fab14930c60e2c" },
   "telescope.nvim": { "branch": "0.1.x", "commit": "a0bbec21143c7bc5f8bb02e0005fa0b982edc026" }
diff --git a/lua/plugins/oil.lua b/lua/plugins/oil.lua
new file mode 100644
index 0000000..685837c
--- /dev/null
+++ b/lua/plugins/oil.lua
@@ -0,0 +1,115 @@
+-- Oil.nvim: file manipulation with buffer sync
+-- Handles rename/move/delete operations that would break buffer names
+-- Use when shell operations would cause buffer issues
+
+return {
+  'stevearc/oil.nvim',
+  lazy = false,
+  keys = {
+    { '<leader>fo', '<cmd>Oil<cr>', desc = 'Open Oil file browser' },
+    { '<leader>fO', '<cmd>Oil --float<cr>', desc = 'Open Oil in floating window' },
+  },
+  opts = {
+    -- Columns shown in the oil buffer
+    columns = {
+      'icon',
+      -- 'permissions',
+      -- 'size',
+      -- 'mtime',
+    },
+    -- Buffer-local options to use for oil buffers
+    buf_options = {
+      buflisted = false,
+      bufhidden = 'hide',
+    },
+    -- Window-local options to use for oil buffers
+    win_options = {
+      wrap = false,
+      signcolumn = 'no',
+      cursorcolumn = false,
+      foldcolumn = '0',
+      spell = false,
+      list = false,
+      conceallevel = 3,
+      concealcursor = 'nvic',
+    },
+    -- Delete to trash instead of permanently deleting
+    delete_to_trash = false,
+    -- Skip confirmation for simple operations
+    skip_confirm_for_simple_edits = false,
+    -- Prompt before deleting a directory
+    prompt_save_on_select_new_entry = true,
+    -- Use default keymaps (see :help oil-actions)
+    use_default_keymaps = true,
+    -- Set to false to disable all of the above keymaps
+    keymaps = {
+      ['g?'] = 'actions.show_help',
+      ['<CR>'] = 'actions.select',
+      ['<C-s>'] = 'actions.select_vsplit',
+      ['<C-h>'] = 'actions.select_split',
+      ['<C-t>'] = 'actions.select_tab',
+      -- Preview opens to the right via vertical split
+      ['<C-p>'] = {
+        'actions.preview',
+        opts = { vertical = true, split = 'belowright' },
+      },
+      ['<C-c>'] = 'actions.close',
+      ['<C-l>'] = 'actions.refresh',
+      ['-'] = 'actions.parent',
+      ['_'] = 'actions.open_cwd',
+      ['`'] = 'actions.cd',
+      ['~'] = 'actions.tcd',
+      ['gs'] = 'actions.change_sort',
+      ['gx'] = 'actions.open_external',
+      ['g.'] = 'actions.toggle_hidden',
+      ['g\\'] = 'actions.toggle_trash',
+    },
+    -- Configuration for the floating window in oil.open_float
+    float = {
+      -- Padding around the floating window
+      padding = 2,
+      max_width = 0,
+      max_height = 0,
+      border = 'rounded',
+      win_options = {
+        winblend = 0,
+      },
+      -- Preview split direction for floating Oil windows
+      preview_split = "right",
+    },
+    -- Configuration for the actions floating preview window
+    preview = {
+      -- Width dimensions can be integers or a float between 0 and 1 (e.g. 0.4 for 40%)
+      max_width = 0.9,
+      -- min_width = {40, 0.4} means "the greater of 40 columns or 40% of total"
+      min_width = { 40, 0.4 },
+      -- optionally define an integer/float for the exact width of the preview window
+      width = nil,
+      -- Height dimensions can be integers or a float between 0 and 1 (e.g. 0.4 for 40%)
+      max_height = 0.9,
+      min_height = { 5, 0.1 },
+      height = nil,
+      border = 'rounded',
+      win_options = {
+        winblend = 0,
+      },
+    },
+    -- Preview split direction: "auto" (floating), "left", "right", "above", "below"
+    -- This setting is deprecated; use keymap opts or float.preview_split instead
+    -- preview_split = "right",
+    -- Configuration for the floating progress window
+    progress = {
+      max_width = 0.9,
+      min_width = { 40, 0.4 },
+      width = nil,
+      max_height = { 10, 0.9 },
+      min_height = { 5, 0.1 },
+      height = nil,
+      border = 'rounded',
+      minimized_border = 'none',
+      win_options = {
+        winblend = 0,
+      },
+    },
+  },
+}