Gate tool calls per command and path, not per tool name

Approval was a list of tool names: `bash` needed it, `read_file` did not. That
fails in a specific way. `bash` covers `git status` and `rm -rf` equally, so a
user working through a batch presses `a` — always allow — on the first prompt and
every later command runs unasked, including the one they would have refused. The
gate was strongest when it mattered least and gone by the time it mattered.

Rules now match the *subject* of a call: the command for `bash`, the path for a
file tool, the pattern for a search.

    "permission": {
      "bash": { "*": "ask", "git *": "allow", "rm *": "deny" },
      "edit_file": { "*": "deny", "src/generated/*": "allow" }
    }

Plain last-match-wins, with no special case for deny. An earlier version made
deny win wherever it sat, on the theory that a refusal should be impossible to
undo by accident, and it made default-deny-with-exceptions unexpressible — which
is the shape a careful user actually writes, and the same shape as `*.env` denied
while `*.env.example` is allowed. Refusals that must never be configurable stay
in the guard plugin, which runs ahead of this and which --yolo cannot reach.

Three behaviours fall out of it:

- `always` grants the pattern the tool suggests, not the tool. Approving
  `git status` runs `git log` unprompted and still asks about `npm publish`.
- `.env`, `.env.*`, and `.pem` are denied on read by default. Not gated, refused:
  a secret that reaches the context is on the wire and in the session file, and
  there is no taking it back. `.env.example` stays allowed.
- A call repeated identically three times in one turn asks even when allowed. A
  model repeating itself is not making progress, and `bash: allow` is a statement
  about which commands are safe rather than permission to loop.

The prompt now says which rule matched and what `always` would grant:

    bash wants to run
    git status --porcelain
    y allow once | a always allow bash git * | n deny

A typo in a decision string is dropped at parse time, leaving the tool on its
default. Treating an unparseable value as `allow` would mean one misspelling
silently removing the gate.

Written after surveying Claude Code, Codex, opencode, and phi. Three of the four
had already moved to per-pattern rules; the credential deny and the repeat guard
come from opencode directly. ROADMAP records what was deliberately not taken and
why — OS sandboxing needs three platform implementations and is worse than
nothing if half-built, and opencode's own docs say LSP integration is often not a
net positive.

581 tests, up from 572. The engine is a pure function tested on its own, and the
loop is tested through a real Session: an allowed pattern never prompts, a denied
one never executes, and a `.env` read leaves no secret in the transcript.

test/session-features.test.ts

@@ -1,6 +1,9 @@
 import { expect, test } from 'bun:test';
 import { MockLanguageModelV4, simulateReadableStream } from 'ai/test';
 import type { LanguageModelV4CallOptions, LanguageModelV4StreamPart } from '@ai-sdk/provider';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
 import { variantByName } from '../src/agents';
 import { Memory } from '../src/memory';
 import { createHost } from '../src/plugins';
@@ -10,6 +13,16 @@ import { loadSkills } from '../src/skills';
 import { MUTATING_TOOLS, TOOL_SETS, TOOL_SET_NAMES, isToolSetName, toolSetOf } from '../src/tools';
 import { GIT_TOOL_NAMES } from '../src/tools-git';
 
+function inTempDir<T>(fn: () => Promise<T>): Promise<T> {
+  const orig = process.cwd();
+  const dir = mkdtempSync(join(tmpdir(), 'shiro-perm-'));
+  process.chdir(dir);
+  return fn().finally(() => {
+    process.chdir(orig);
+    rmSync(dir, { recursive: true, force: true });
+  });
+}
+
 const usage = {
   inputTokens: { total: 5, noCache: 5, cacheRead: 0, cacheWrite: 0 },
   outputTokens: { total: 2 },
@@ -296,3 +309,218 @@ test('isToolSetName accepts the real sets only, so a typo in config is ignored',
   for (const name of TOOL_SET_NAMES) expect(isToolSetName(name)).toBe(true);
   expect(isToolSetName('gti')).toBe(false);
 });
+
+const bashCall = (id: string, command: string) => toolCall(id, 'bash', { command });
+
+test('a pattern that allows skips the prompt entirely', async () => {
+  let n = 0;
+  const session = new Session({
+    model: new MockLanguageModelV4({
+      doStream: async () => (n++ === 0 ? stream(bashCall('c1', 'echo allowed')) : stream(text('done'))),
+    }),
+    askApproval: async () => {
+      throw new Error('an allowed pattern must not prompt');
+    },
+    permissions: { bash: { '*': 'ask', 'echo *': 'allow' } },
+  });
+
+  const kinds: string[] = [];
+  for await (const ev of session.send('say something')) kinds.push(ev.type);
+  expect(kinds).toContain('tool-result');
+  expect(kinds).not.toContain('tool-denied');
+});
+
+test('a pattern that denies refuses without asking, and the tool never runs', async () =>
+  inTempDir(async () => {
+    let asked = 0;
+    let n = 0;
+    const session = new Session({
+      model: new MockLanguageModelV4({
+        doStream: async () =>
+          n++ === 0 ? stream(bashCall('c1', 'rm -rf build > out.txt')) : stream(text('understood')),
+      }),
+      askApproval: async () => {
+        asked++;
+        return 'once';
+      },
+      // Deliberately not the guard plugin: this is the rule engine refusing.
+      plugins: undefined,
+      permissions: { bash: { '*': 'ask', 'rm *': 'deny' } },
+    });
+
+    const events: string[] = [];
+    const notices: string[] = [];
+    for await (const ev of session.send('clean up')) {
+      events.push(ev.type);
+      if (ev.type === 'notice') notices.push(ev.text);
+    }
+
+    expect(asked).toBe(0);
+    expect(events).toContain('tool-denied');
+    expect(notices.join()).toContain('"rm *" = deny');
+    expect(await Bun.file(join(process.cwd(), 'out.txt')).exists()).toBe(false);
+  }));
+
+test('a command outside the allowed pattern still asks', async () => {
+  const asked: string[] = [];
+  let n = 0;
+  const session = new Session({
+    model: new MockLanguageModelV4({
+      doStream: async () => (n++ === 0 ? stream(bashCall('c1', 'npm publish')) : stream(text('done'))),
+    }),
+    askApproval: async (req) => {
+      asked.push(req.toolName);
+      return 'deny';
+    },
+    permissions: { bash: { '*': 'ask', 'git *': 'allow' } },
+  });
+
+  for await (const _ of session.send('publish it')) void _;
+  expect(asked).toEqual(['bash']);
+});
+
+test('always records the suggested pattern, so a sibling command runs unprompted', async () => {
+  const asked: string[] = [];
+  let n = 0;
+  const session = new Session({
+    model: new MockLanguageModelV4({
+      doStream: async () => {
+        const i = n++;
+        if (i === 0) return stream(bashCall('c1', 'git status'));
+        if (i === 1) return stream(bashCall('c2', 'git log'));
+        if (i === 2) return stream(bashCall('c3', 'npm test'));
+        return stream(text('done'));
+      },
+    }),
+    askApproval: async (req) => {
+      asked.push(String((req.input as { command?: string }).command));
+      return req.suggestedPattern === 'git *' ? 'always' : 'deny';
+    },
+  });
+
+  for await (const _ of session.send('inspect the repo')) void _;
+
+  // git status is approved as `git *`, so git log never reaches the prompt.
+  expect(asked).toEqual(['git status', 'npm test']);
+});
+
+test('the prompt carries the pattern that matched and what always would grant', async () => {
+  const seen: { matched?: string; suggested: string }[] = [];
+  let n = 0;
+  const session = new Session({
+    model: new MockLanguageModelV4({
+      doStream: async () => (n++ === 0 ? stream(bashCall('c1', 'npm test')) : stream(text('done'))),
+    }),
+    askApproval: async (req) => {
+      seen.push({ ...(req.matchedPattern ? { matched: req.matchedPattern } : {}), suggested: req.suggestedPattern });
+      return 'deny';
+    },
+    permissions: { bash: { '*': 'ask' } },
+  });
+
+  for await (const _ of session.send('test it')) void _;
+  expect(seen).toEqual([{ matched: '*', suggested: 'npm *' }]);
+});
+
+test('a third identical call is asked about even when the rules allow it', async () =>
+  inTempDir(async () => {
+    await Bun.write(join(process.cwd(), 'note.txt'), 'hello');
+
+    const asked: boolean[] = [];
+    let n = 0;
+    const session = new Session({
+      model: new MockLanguageModelV4({
+        doStream: async () => {
+          const i = n++;
+          return i < 4 ? stream(toolCall(`c${i}`, 'read_file', { path: 'note.txt' })) : stream(text('done'));
+        },
+      }),
+      askApproval: async (req) => {
+        asked.push(req.repeated === true);
+        return 'once';
+      },
+    });
+
+    for await (const _ of session.send('read it repeatedly')) void _;
+
+    // Two identical reads pass; the third and fourth are asked about, flagged as
+    // repeats rather than as rule matches.
+    expect(asked).toEqual([true, true]);
+  }));
+
+test('the repeat guard counts per turn, not for the life of the session', async () =>
+  inTempDir(async () => {
+    await Bun.write(join(process.cwd(), 'note.txt'), 'hello');
+
+    let asks = 0;
+    let n = 0;
+    const session = new Session({
+      model: new MockLanguageModelV4({
+        doStream: async () => {
+          const i = n++ % 3;
+          return i < 2 ? stream(toolCall(`c${i}`, 'read_file', { path: 'note.txt' })) : stream(text('done'));
+        },
+      }),
+      askApproval: async () => {
+        asks++;
+        return 'once';
+      },
+    });
+
+    for await (const _ of session.send('first turn')) void _;
+    for await (const _ of session.send('second turn')) void _;
+
+    // Two reads per turn, twice: never three in one turn, so never asked.
+    expect(asks).toBe(0);
+  }));
+
+test('the guard plugin still refuses ahead of the rules, and yolo cannot reach it', async () => {
+  let asked = 0;
+  let n = 0;
+  const session = new Session({
+    yolo: true,
+    model: new MockLanguageModelV4({
+      doStream: async () => (n++ === 0 ? stream(bashCall('c1', 'rm -rf /')) : stream(text('understood'))),
+    }),
+    askApproval: async () => {
+      asked++;
+      return 'once';
+    },
+    plugins: createHost([guardPlugin]),
+    permissions: { bash: 'allow' },
+  });
+
+  const notices: string[] = [];
+  for await (const ev of session.send('clean up')) if (ev.type === 'notice') notices.push(ev.text);
+
+  expect(asked).toBe(0);
+  expect(notices.join()).toContain('recursive or forced delete');
+});
+
+test('reading a credential is refused by default', async () =>
+  inTempDir(async () => {
+    await Bun.write(join(process.cwd(), '.env'), 'SECRET=hunter2');
+
+    let n = 0;
+    const session = new Session({
+      model: new MockLanguageModelV4({
+        doStream: async () => (n++ === 0 ? stream(toolCall('c1', 'read_file', { path: '.env' })) : stream(text('ok'))),
+      }),
+      askApproval: async () => {
+        throw new Error('a denied read must not prompt');
+      },
+    });
+
+    const events: string[] = [];
+    const notices: string[] = [];
+    for await (const ev of session.send('read the env file')) {
+      events.push(ev.type);
+      if (ev.type === 'notice') notices.push(ev.text);
+    }
+
+    expect(events).toContain('tool-denied');
+    expect(notices.join()).toContain('deny');
+    // The secret must not reach the transcript either.
+    expect(JSON.stringify(session.messages)).not.toContain('hunter2');
+  }));
+