feat: add tool-level file cache with LRU eviction and mtime invalidation

Introduces FileCache (OrderedDict LRU, st_mtime_ns validation) to avoid
redundant disk reads and duplicate content in conversation context.
Read tools return a short "[Cached]" message on cache hit instead of
resending unchanged file content, saving tokens. Write/edit/delete tools
invalidate affected paths; str_replace pre-warms the cache after edits.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/models/config.py

@@ -73,11 +73,19 @@ class ShellToolConfig(BaseModel):
     max_output_bytes: int = Field(default=65536, description="Max output capture size in bytes")
 
 
+class FileCacheConfig(BaseModel):
+    """File cache configuration."""
+
+    enabled: bool = Field(default=True, description="Enable file content caching")
+    max_entries: int = Field(default=128, description="Maximum cached file entries (LRU eviction)")
+
+
 class FilesystemToolConfig(BaseModel):
     """Filesystem tool limits."""
 
     max_file_size_bytes: int = Field(default=1_048_576, description="Max file size for read/write")
     binary_detection: bool = Field(default=True, description="Detect and reject binary files")
+    cache: FileCacheConfig = Field(default_factory=FileCacheConfig, description="File cache settings")
 
 
 class ToolsConfig(BaseModel):

app/tools/edit.py

@@ -1,13 +1,17 @@
 """Edit tools: str_replace and patch_apply."""
 
+from __future__ import annotations
+
 import subprocess
 from pathlib import Path
 from typing import Any
 
 from pydantic import BaseModel, Field
 
+from app.models.config import AppConfig
 from app.models.tool_call import ToolResult, ToolResultStatus
 from app.tools.base import BaseTool
+from app.utils.file_cache import FileCache, cached_read_file
 from app.utils.file_helpers import (
     FileSizeError,
     PathSecurityError,
@@ -37,6 +41,12 @@ class StrReplaceTool(BaseTool):
     )
     params_model = StrReplaceParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(
         self, *, tool_call_id: str, file_path: str, old_str: str, new_str: str, **kwargs: Any
     ) -> ToolResult:
@@ -44,11 +54,12 @@ class StrReplaceTool(BaseTool):
 
         # Read the file
         try:
-            content = safe_read_file(
+            content = cached_read_file(
                 file_path,
                 self.workspace_root,
                 max_size_bytes=fs_config.max_file_size_bytes,
                 check_binary=fs_config.binary_detection,
+                cache=self._file_cache,
             )
         except PathSecurityError as exc:
             return ToolResult(
@@ -117,8 +128,14 @@ class StrReplaceTool(BaseTool):
             safe_path = resolve_safe_path(file_path, self.workspace_root)
             rel_path = safe_path.relative_to(self.workspace_root)
         except (PathSecurityError, ValueError):
+            safe_path = None
             rel_path = Path(file_path)
 
+        # Pre-warm cache with the new content (we already have it in memory).
+        if self._file_cache is not None and safe_path is not None:
+            self._file_cache.invalidate(safe_path)
+            self._file_cache.put(safe_path, new_content)
+
         return ToolResult(
             tool_call_id=tool_call_id,
             tool_name=self.name,
@@ -144,6 +161,12 @@ class PatchApplyTool(BaseTool):
     )
     params_model = PatchApplyParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(self, *, tool_call_id: str, file_path: str, patch: str, **kwargs: Any) -> ToolResult:
         try:
             safe_path = resolve_safe_path(file_path, self.workspace_root)
@@ -195,6 +218,9 @@ class PatchApplyTool(BaseTool):
                 error=f"Patch failed (exit {result.returncode}): {result.stderr or result.stdout}",
             )
 
+        if self._file_cache is not None:
+            self._file_cache.invalidate(safe_path)
+
         try:
             rel_path = safe_path.relative_to(self.workspace_root)
         except ValueError:

app/tools/filesystem.py

@@ -1,12 +1,16 @@
 """Filesystem tools: read_file, list_dir, write_file, make_dir, delete_file."""
 
+from __future__ import annotations
+
 from pathlib import Path
 from typing import Any
 
 from pydantic import BaseModel, Field
 
+from app.models.config import AppConfig
 from app.models.tool_call import ToolResult, ToolResultStatus
 from app.tools.base import BaseTool
+from app.utils.file_cache import FileCache, cached_read_file
 from app.utils.file_helpers import (
     BinaryFileError,
     FileSizeError,
@@ -36,14 +40,22 @@ class ReadFileTool(BaseTool):
     description = "Read the full contents of a text file. Returns the file content as a string."
     params_model = ReadFileParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(self, *, tool_call_id: str, file_path: str, **kwargs: Any) -> ToolResult:
         fs_config = self.config.tools.filesystem
+        hits_before = self._file_cache.stats.hits if self._file_cache else 0
         try:
-            content = safe_read_file(
+            content = cached_read_file(
                 file_path,
                 self.workspace_root,
                 max_size_bytes=fs_config.max_file_size_bytes,
                 check_binary=fs_config.binary_detection,
+                cache=self._file_cache,
             )
         except PathSecurityError as exc:
             return ToolResult(
@@ -74,6 +86,23 @@ class ReadFileTool(BaseTool):
                 error=str(exc),
             )
 
+        # On cache hit the file is unchanged — its content is already in
+        # conversation context from the earlier read, so avoid resending it.
+        was_cache_hit = (
+            self._file_cache is not None
+            and self._file_cache.stats.hits > hits_before
+        )
+        if was_cache_hit:
+            return ToolResult(
+                tool_call_id=tool_call_id,
+                tool_name=self.name,
+                status=ToolResultStatus.SUCCESS,
+                output=(
+                    f"[Cached] {file_path} is unchanged since last read "
+                    f"({len(content):,} chars). Content is already in conversation context."
+                ),
+            )
+
         return ToolResult(
             tool_call_id=tool_call_id,
             tool_name=self.name,
@@ -92,6 +121,12 @@ class ReadManyFilesTool(BaseTool):
     )
     params_model = ReadManyFilesParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(self, *, tool_call_id: str, file_paths: list[str], **kwargs: Any) -> ToolResult:
         if not file_paths:
             return ToolResult(
@@ -106,14 +141,26 @@ class ReadManyFilesTool(BaseTool):
         success_count = 0
 
         for fp in file_paths:
+            hits_before = self._file_cache.stats.hits if self._file_cache else 0
             try:
-                content = safe_read_file(
+                content = cached_read_file(
                     fp,
                     self.workspace_root,
                     max_size_bytes=fs_config.max_file_size_bytes,
                     check_binary=fs_config.binary_detection,
+                    cache=self._file_cache,
                 )
-                sections.append(f"=== {fp} ===\n{content}")
+                was_hit = (
+                    self._file_cache is not None
+                    and self._file_cache.stats.hits > hits_before
+                )
+                if was_hit:
+                    sections.append(
+                        f"=== {fp} ===\n[Cached] Unchanged since last read "
+                        f"({len(content):,} chars). Already in conversation context."
+                    )
+                else:
+                    sections.append(f"=== {fp} ===\n{content}")
                 success_count += 1
             except (PathSecurityError, FileNotFoundError, FileSizeError, BinaryFileError) as exc:
                 sections.append(f"=== {fp} ===\n[ERROR] {exc}")
@@ -225,6 +272,12 @@ class WriteFileTool(BaseTool):
     )
     params_model = WriteFileParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(self, *, tool_call_id: str, file_path: str, content: str, **kwargs: Any) -> ToolResult:
         fs_config = self.config.tools.filesystem
         try:
@@ -249,6 +302,9 @@ class WriteFileTool(BaseTool):
                 error=str(exc),
             )
 
+        if self._file_cache is not None:
+            self._file_cache.invalidate(safe_path)
+
         try:
             rel_path = safe_path.relative_to(self.workspace_root)
         except ValueError:
@@ -330,6 +386,12 @@ class DeleteFileTool(BaseTool):
     description = "Delete a single file. Does not delete directories."
     params_model = DeleteFileParams
 
+    def __init__(
+        self, workspace_root: Path, config: AppConfig, file_cache: FileCache | None = None
+    ) -> None:
+        super().__init__(workspace_root, config)
+        self._file_cache = file_cache
+
     def execute(self, *, tool_call_id: str, file_path: str, **kwargs: Any) -> ToolResult:
         try:
             safe_path = resolve_safe_path(file_path, self.workspace_root)
@@ -367,6 +429,9 @@ class DeleteFileTool(BaseTool):
                 error=f"Failed to delete file: {exc}",
             )
 
+        if self._file_cache is not None:
+            self._file_cache.invalidate(safe_path)
+
         try:
             rel_path = safe_path.relative_to(self.workspace_root)
         except ValueError:

app/tools/registry.py

@@ -8,6 +8,7 @@ from typing import TYPE_CHECKING, Any
 
 from app.models.config import AppConfig
 from app.tools.base import BaseTool
+from app.utils.file_cache import FileCache
 
 if TYPE_CHECKING:
     from app.services.skills import SkillsManager
@@ -89,6 +90,7 @@ def create_default_registry(
     config: AppConfig,
     skills_manager: SkillsManager | None = None,
     skill_runner: object | None = None,
+    file_cache: FileCache | None = None,
 ) -> ToolRegistry:
     """Create a ToolRegistry populated with all built-in tools.
 
@@ -97,6 +99,7 @@ def create_default_registry(
         config: Application configuration.
         skills_manager: Optional skills manager for skill tools.
         skill_runner: Optional SkillRunner for package skill activation.
+        file_cache: Optional file cache shared across file-reading tools.
     """
     # Read tools
     from app.tools.filesystem import ListDirTool, ReadFileTool, ReadManyFilesTool
@@ -119,8 +122,8 @@ def create_default_registry(
     registry = ToolRegistry()
 
     # Read
-    registry.register(ReadFileTool(workspace_root, config))
+    registry.register(ReadFileTool(workspace_root, config, file_cache=file_cache))
-    registry.register(ReadManyFilesTool(workspace_root, config))
+    registry.register(ReadManyFilesTool(workspace_root, config, file_cache=file_cache))
     registry.register(ListDirTool(workspace_root, config))
 
     # Search
@@ -128,13 +131,13 @@ def create_default_registry(
     registry.register(FindFilesTool(workspace_root, config))
 
     # Write
-    registry.register(WriteFileTool(workspace_root, config))
+    registry.register(WriteFileTool(workspace_root, config, file_cache=file_cache))
     registry.register(MakeDirTool(workspace_root, config))
-    registry.register(DeleteFileTool(workspace_root, config))
+    registry.register(DeleteFileTool(workspace_root, config, file_cache=file_cache))
 
     # Edit
-    registry.register(StrReplaceTool(workspace_root, config))
+    registry.register(StrReplaceTool(workspace_root, config, file_cache=file_cache))
-    registry.register(PatchApplyTool(workspace_root, config))
+    registry.register(PatchApplyTool(workspace_root, config, file_cache=file_cache))
 
     # Shell
     registry.register(RunCommandTool(workspace_root, config))

app/ui/app.py

@@ -97,11 +97,20 @@ class SneakyCodeApp(App):
                 self._config.skills, self._config.agent.workspace_root
             )
 
+        # Create file cache if enabled
+        self._file_cache = None
+        fs_cache_cfg = self._config.tools.filesystem.cache
+        if fs_cache_cfg.enabled:
+            from app.utils.file_cache import FileCache
+
+            self._file_cache = FileCache(max_entries=fs_cache_cfg.max_entries)
+
         # Create tool registry (SkillRunner wired after registry exists)
         self._tool_registry = create_default_registry(
             self._config.agent.workspace_root,
             self._config,
             skills_manager=self._skills_manager,
+            file_cache=self._file_cache,
         )
 
         # Create SkillRunner and late-bind it to skill tools

app/utils/file_cache.py

@@ -0,0 +1,185 @@
+"""File cache with LRU eviction and mtime-based invalidation."""
+
+from __future__ import annotations
+
+from collections import OrderedDict
+from dataclasses import dataclass, field
+from pathlib import Path
+
+from app.utils.file_helpers import (
+    BinaryFileError,
+    FileSizeError,
+    PathSecurityError,
+    check_file_size,
+    is_binary_file,
+    resolve_safe_path,
+)
+
+
+@dataclass(slots=True)
+class CacheEntry:
+    """A cached file's content and modification timestamp."""
+
+    content: str
+    mtime_ns: int
+
+
+@dataclass
+class CacheStats:
+    """Running statistics for a FileCache instance."""
+
+    hits: int = 0
+    misses: int = 0
+    invalidations: int = 0
+    evictions: int = 0
+
+    @property
+    def hit_rate(self) -> float:
+        """Return cache hit rate as a float between 0.0 and 1.0."""
+        total = self.hits + self.misses
+        if total == 0:
+            return 0.0
+        return self.hits / total
+
+
+class FileCache:
+    """LRU file-content cache with mtime-based invalidation.
+
+    Keyed by resolved absolute ``Path``.  Each lookup performs a cheap
+    ``stat()`` syscall to verify the file hasn't changed on disk — if the
+    nanosecond mtime differs the entry is evicted and the caller gets a
+    cache miss.
+
+    Not thread-safe (single-threaded agent loop).
+    """
+
+    def __init__(self, max_entries: int = 128) -> None:
+        self._max_entries = max_entries
+        self._entries: OrderedDict[Path, CacheEntry] = OrderedDict()
+        self._stats = CacheStats()
+
+    # -- public API --------------------------------------------------
+
+    def get(self, path: Path) -> str | None:
+        """Return cached content if *path* hasn't changed, else ``None``.
+
+        A ``stat()`` call checks ``st_mtime_ns``; on mismatch the stale
+        entry is silently removed.
+        """
+        entry = self._entries.get(path)
+        if entry is None:
+            self._stats.misses += 1
+            return None
+
+        try:
+            current_mtime_ns = path.stat().st_mtime_ns
+        except OSError:
+            # File gone — evict and miss.
+            self._remove(path)
+            self._stats.misses += 1
+            return None
+
+        if current_mtime_ns != entry.mtime_ns:
+            self._remove(path)
+            self._stats.invalidations += 1
+            self._stats.misses += 1
+            return None
+
+        # Cache hit — move to end (most-recently used).
+        self._entries.move_to_end(path)
+        self._stats.hits += 1
+        return entry.content
+
+    def put(self, path: Path, content: str) -> None:
+        """Store *content* for *path* with its current ``st_mtime_ns``.
+
+        Evicts the least-recently-used entry when over capacity.
+        """
+        try:
+            mtime_ns = path.stat().st_mtime_ns
+        except OSError:
+            # Can't stat — don't cache.
+            return
+
+        if path in self._entries:
+            # Update existing; move to end.
+            self._entries[path] = CacheEntry(content=content, mtime_ns=mtime_ns)
+            self._entries.move_to_end(path)
+        else:
+            self._entries[path] = CacheEntry(content=content, mtime_ns=mtime_ns)
+
+        # Evict LRU if over capacity.
+        while len(self._entries) > self._max_entries:
+            self._entries.popitem(last=False)
+            self._stats.evictions += 1
+
+    def invalidate(self, path: Path) -> None:
+        """Remove *path* from the cache if present."""
+        if path in self._entries:
+            del self._entries[path]
+            self._stats.invalidations += 1
+
+    def clear(self) -> None:
+        """Remove all entries."""
+        self._entries.clear()
+
+    @property
+    def stats(self) -> CacheStats:
+        """Return the running cache statistics."""
+        return self._stats
+
+    def __len__(self) -> int:
+        return len(self._entries)
+
+    # -- internals ---------------------------------------------------
+
+    def _remove(self, path: Path) -> None:
+        """Delete an entry without bumping invalidation stats."""
+        self._entries.pop(path, None)
+
+
+def cached_read_file(
+    path: str | Path,
+    workspace_root: Path,
+    max_size_bytes: int = 1_048_576,
+    check_binary: bool = True,
+    cache: FileCache | None = None,
+) -> str:
+    """Read a file with full security checks, using *cache* when available.
+
+    Security checks (path sandboxing, size limit, binary detection) run on
+    **every** call — only the ``Path.read_text()`` I/O is skipped on a cache
+    hit.
+
+    When *cache* is ``None`` this behaves identically to
+    :func:`~app.utils.file_helpers.safe_read_file`.
+
+    Raises:
+        PathSecurityError: If the path escapes the workspace.
+        FileSizeError: If the file is too large.
+        BinaryFileError: If the file is binary and *check_binary* is True.
+        FileNotFoundError: If the file does not exist.
+    """
+    safe_path = resolve_safe_path(path, workspace_root)
+
+    if not safe_path.exists():
+        raise FileNotFoundError(f"File not found: {safe_path}")
+
+    check_file_size(safe_path, max_size_bytes)
+
+    if check_binary and is_binary_file(safe_path):
+        raise BinaryFileError(f"File appears to be binary: {safe_path}")
+
+    # Try cache.
+    if cache is not None:
+        cached = cache.get(safe_path)
+        if cached is not None:
+            return cached
+
+    # Cache miss (or no cache) — read from disk.
+    content = safe_path.read_text(encoding="utf-8")
+
+    if cache is not None:
+        cache.put(safe_path, content)
+
+    return content

config/config.yaml

@@ -68,6 +68,9 @@ tools:
   filesystem:
     max_file_size_bytes: 1048576  # 1 MB
     binary_detection: true
+    cache:
+      enabled: true
+      max_entries: 128
 
 session:
   session_dir: ".sneakycode/sessions"

tests/unit/test_file_cache.py

@@ -0,0 +1,314 @@
+"""Tests for the file cache with LRU eviction and mtime invalidation."""
+
+import os
+import time
+from pathlib import Path
+
+import pytest
+
+from app.models.config import AppConfig, load_config
+from app.models.tool_call import ToolResultStatus
+from app.tools.filesystem import ReadFileTool, ReadManyFilesTool
+from app.utils.file_cache import CacheStats, FileCache, cached_read_file
+from app.utils.file_helpers import BinaryFileError, FileSizeError, PathSecurityError
+
+
+# ---------------------------------------------------------------------------
+# FileCache unit tests
+# ---------------------------------------------------------------------------
+
+
+class TestFileCache:
+    def test_put_and_get_roundtrip(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "hello.txt"
+        f.write_text("hello world")
+
+        cache.put(f, "hello world")
+        assert cache.get(f) == "hello world"
+
+    def test_get_returns_none_for_missing_key(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        assert cache.get(tmp_path / "nope.txt") is None
+
+    def test_mtime_change_causes_miss(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "data.txt"
+        f.write_text("v1")
+        cache.put(f, "v1")
+
+        # Mutate the file so mtime changes
+        time.sleep(0.05)  # ensure mtime differs
+        f.write_text("v2")
+
+        assert cache.get(f) is None  # stale → miss
+        assert cache.stats.invalidations == 1
+
+    def test_lru_eviction_at_capacity(self, tmp_path: Path) -> None:
+        cache = FileCache(max_entries=3)
+        files = []
+        for i in range(4):
+            f = tmp_path / f"f{i}.txt"
+            f.write_text(f"content-{i}")
+            files.append(f)
+
+        # Fill cache to capacity
+        for f in files[:3]:
+            cache.put(f, f.read_text())
+        assert len(cache) == 3
+
+        # Adding a 4th evicts the LRU (files[0])
+        cache.put(files[3], files[3].read_text())
+        assert len(cache) == 3
+        assert cache.get(files[0]) is None  # evicted
+        assert cache.stats.evictions == 1
+
+        # files[1..3] still present
+        for f in files[1:]:
+            assert cache.get(f) is not None
+
+    def test_invalidate_removes_entry(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "rm.txt"
+        f.write_text("bye")
+        cache.put(f, "bye")
+        assert len(cache) == 1
+
+        cache.invalidate(f)
+        assert len(cache) == 0
+        assert cache.get(f) is None
+        assert cache.stats.invalidations == 1
+
+    def test_invalidate_noop_for_missing(self) -> None:
+        cache = FileCache()
+        cache.invalidate(Path("/nonexistent"))
+        assert cache.stats.invalidations == 0
+
+    def test_clear_empties_cache(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        for i in range(5):
+            f = tmp_path / f"c{i}.txt"
+            f.write_text(str(i))
+            cache.put(f, str(i))
+        assert len(cache) == 5
+
+        cache.clear()
+        assert len(cache) == 0
+
+    def test_stats_accuracy(self, tmp_path: Path) -> None:
+        cache = FileCache(max_entries=2)
+        a = tmp_path / "a.txt"
+        b = tmp_path / "b.txt"
+        c = tmp_path / "c.txt"
+        a.write_text("a")
+        b.write_text("b")
+        c.write_text("c")
+
+        # Miss
+        cache.get(a)
+        assert cache.stats.misses == 1
+        assert cache.stats.hits == 0
+
+        # Put + hit
+        cache.put(a, "a")
+        cache.get(a)
+        assert cache.stats.hits == 1
+
+        # Fill + evict
+        cache.put(b, "b")
+        cache.put(c, "c")  # evicts a
+        assert cache.stats.evictions == 1
+
+    def test_hit_rate(self) -> None:
+        stats = CacheStats(hits=3, misses=1)
+        assert stats.hit_rate == pytest.approx(0.75)
+
+    def test_hit_rate_zero_total(self) -> None:
+        stats = CacheStats()
+        assert stats.hit_rate == 0.0
+
+    def test_file_deleted_after_caching(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "gone.txt"
+        f.write_text("here")
+        cache.put(f, "here")
+
+        f.unlink()
+        assert cache.get(f) is None  # stat fails → miss
+
+    def test_put_skips_when_stat_fails(self) -> None:
+        cache = FileCache()
+        cache.put(Path("/totally/nonexistent"), "data")
+        assert len(cache) == 0
+
+    def test_get_moves_to_end(self, tmp_path: Path) -> None:
+        """Accessing an entry makes it most-recently-used, protecting from eviction."""
+        cache = FileCache(max_entries=3)
+        files = []
+        for i in range(3):
+            f = tmp_path / f"lru{i}.txt"
+            f.write_text(f"c{i}")
+            files.append(f)
+            cache.put(f, f"c{i}")
+
+        # Touch files[0] to make it MRU
+        cache.get(files[0])
+
+        # Add a new entry — files[1] (LRU) should be evicted, not files[0]
+        extra = tmp_path / "extra.txt"
+        extra.write_text("x")
+        cache.put(extra, "x")
+
+        assert cache.get(files[0]) is not None  # protected by access
+        assert cache.get(files[1]) is None  # evicted
+
+
+# ---------------------------------------------------------------------------
+# cached_read_file tests
+# ---------------------------------------------------------------------------
+
+
+class TestCachedReadFile:
+    def test_without_cache_matches_safe_read(self, tmp_path: Path) -> None:
+        f = tmp_path / "plain.txt"
+        f.write_text("hello")
+        content = cached_read_file(f, tmp_path, cache=None)
+        assert content == "hello"
+
+    def test_populates_on_miss_returns_on_hit(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "cached.txt"
+        f.write_text("data")
+
+        # First call: miss → read from disk → populate cache
+        content1 = cached_read_file(f, tmp_path, cache=cache)
+        assert content1 == "data"
+        assert cache.stats.misses == 1
+        assert cache.stats.hits == 0
+
+        # Second call: hit → from cache
+        content2 = cached_read_file(f, tmp_path, cache=cache)
+        assert content2 == "data"
+        assert cache.stats.hits == 1
+
+    def test_security_checks_run_on_cached_path(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        with pytest.raises(PathSecurityError):
+            cached_read_file("/etc/passwd", tmp_path, cache=cache)
+
+    def test_binary_check_runs_on_cached_path(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "bin.dat"
+        f.write_bytes(b"\x00binary\x00")
+        with pytest.raises(BinaryFileError):
+            cached_read_file(f, tmp_path, cache=cache)
+
+    def test_size_check_runs_on_cached_path(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        f = tmp_path / "big.txt"
+        f.write_text("x" * 200)
+
+        # First read populates cache
+        cached_read_file(f, tmp_path, max_size_bytes=1000, cache=cache)
+
+        # Now make file too big on disk — security check should catch it
+        # even though content is cached
+        f.write_text("x" * 2000)
+        with pytest.raises(FileSizeError):
+            cached_read_file(f, tmp_path, max_size_bytes=1000, cache=cache)
+
+    def test_file_not_found(self, tmp_path: Path) -> None:
+        cache = FileCache()
+        with pytest.raises(FileNotFoundError):
+            cached_read_file(tmp_path / "nope.txt", tmp_path, cache=cache)
+
+
+# ---------------------------------------------------------------------------
+# Tool-level cache-hit dedup tests
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def config() -> AppConfig:
+    return load_config()
+
+
+@pytest.fixture
+def tmp_workspace(tmp_path: Path, config: AppConfig) -> tuple[Path, AppConfig]:
+    config.agent.workspace_root = tmp_path
+    return tmp_path, config
+
+
+class TestReadFileToolCacheHit:
+    def test_first_read_returns_full_content(self, tmp_workspace: tuple[Path, AppConfig]) -> None:
+        ws, cfg = tmp_workspace
+        cache = FileCache()
+        (ws / "hello.txt").write_text("hello world")
+
+        tool = ReadFileTool(ws, cfg, file_cache=cache)
+        result = tool.run("tc-1", {"file_path": "hello.txt"})
+        assert result.status == ToolResultStatus.SUCCESS
+        assert result.output == "hello world"
+
+    def test_second_read_returns_cached_message(self, tmp_workspace: tuple[Path, AppConfig]) -> None:
+        ws, cfg = tmp_workspace
+        cache = FileCache()
+        (ws / "hello.txt").write_text("hello world")
+
+        tool = ReadFileTool(ws, cfg, file_cache=cache)
+        tool.run("tc-1", {"file_path": "hello.txt"})
+
+        result2 = tool.run("tc-2", {"file_path": "hello.txt"})
+        assert result2.status == ToolResultStatus.SUCCESS
+        assert "[Cached]" in result2.output
+        assert "hello.txt" in result2.output
+        assert "hello world" not in result2.output
+
+    def test_changed_file_returns_full_content_again(self, tmp_workspace: tuple[Path, AppConfig]) -> None:
+        ws, cfg = tmp_workspace
+        cache = FileCache()
+        f = ws / "data.txt"
+        f.write_text("v1")
+
+        tool = ReadFileTool(ws, cfg, file_cache=cache)
+        tool.run("tc-1", {"file_path": "data.txt"})
+
+        # Mutate file so mtime changes
+        time.sleep(0.05)
+        f.write_text("v2")
+
+        result2 = tool.run("tc-2", {"file_path": "data.txt"})
+        assert result2.status == ToolResultStatus.SUCCESS
+        assert result2.output == "v2"
+        assert "[Cached]" not in result2.output
+
+    def test_no_cache_always_returns_content(self, tmp_workspace: tuple[Path, AppConfig]) -> None:
+        ws, cfg = tmp_workspace
+        (ws / "hello.txt").write_text("hello")
+
+        tool = ReadFileTool(ws, cfg, file_cache=None)
+        r1 = tool.run("tc-1", {"file_path": "hello.txt"})
+        r2 = tool.run("tc-2", {"file_path": "hello.txt"})
+        assert r1.output == "hello"
+        assert r2.output == "hello"
+
+
+class TestReadManyFilesToolCacheHit:
+    def test_cached_files_get_short_message(self, tmp_workspace: tuple[Path, AppConfig]) -> None:
+        ws, cfg = tmp_workspace
+        cache = FileCache()
+        (ws / "a.txt").write_text("alpha")
+        (ws / "b.txt").write_text("bravo")
+
+        tool = ReadManyFilesTool(ws, cfg, file_cache=cache)
+
+        # First read — full content
+        r1 = tool.run("tc-1", {"file_paths": ["a.txt", "b.txt"]})
+        assert "alpha" in r1.output
+        assert "bravo" in r1.output
+
+        # Second read — cached messages
+        r2 = tool.run("tc-2", {"file_paths": ["a.txt", "b.txt"]})
+        assert "[Cached]" in r2.output
+        assert "alpha" not in r2.output
+        assert "bravo" not in r2.output