Compress system prompt and tool descriptions for token efficiency

Reduces per-turn token cost of prompt and tool metadata by ~2,160
tokens (~8.6 KB across 12 prompt files) without losing instructional
signal. Moves literal default values from description text into
TypeBox's native `default:` keyword, and updates the strict-mode
sanitizer to preserve default info for providers that strip the
keyword.

Prompt compression

|File                                      |before |after  |delta |
|------------------------------------------|------:|------:|-----:|
|system-prompt.md                          |25,605 |21,530 |−16%  |
|prompts/tools/ast-grep.md                 | 4,892 | 3,880 |−21%  |
|prompts/tools/ast-edit.md                 | 4,141 | 3,549 |−14%  |
|prompts/tools/bash.md                     | 3,770 | 3,093 |−18%  |
|prompts/tools/task.md                     | 7,297 | 6,711 |−8%   |
|prompts/tools/read.md                     | 2,701 | 2,309 |−15%  |
|prompts/tools/debug.md                    | 2,791 | 2,412 |−14%  |
|prompts/tools/find.md                     |   860 |   561 |−35%  |
|prompts/tools/grep.md                     | 1,226 | 1,038 |−15%  |
|prompts/tools/todo-write.md               | 2,600 | 2,402 |−8%   |
|prompts/tools/python.md                   | 2,013 | 1,916 |−5%   |
|prompts/tools/hashline.md                 | 4,280 | 4,135 |−3%   |

Changes are textual compression only — grammar-scaffolding removed,
redundant bullets stripped, repeated facts consolidated. All
behavioral contracts, safety rules, worked examples, and
tool-precedence directives are preserved. The system prompt retains
RFC 2119 invocation, XML tag semantics, adversarial-caller guidance,
persistence doctrine, unit-of-change and no-forwarding-addresses
rules, completeness contract, DRY-at-2, earn-every-line, trust-
internal-code, tool precedence, AST tool priority, pattern-syntax
cheatsheet (via ast-grep.md/ast-edit.md), tool persistence,
outside-in code integrity, default follow-through, and procedural
steps 1-7. AST tool docs retain the class-wrapper +
method_definition sel example (the most error-prone usage pattern).
bash.md critical section retains MUST-weight on the ast_grep /
ast_edit directives.

Schema: defaults as first-class metadata

Moved 18 literal default values from `(default: X)` description
text into TypeBox's native `default:` keyword across:
ast-edit.ts, ast-grep.ts, bash.ts, browser.ts, find.ts, gh.ts,
grep.ts, python.ts, read.ts, ssh.ts. Runtime-resolved placeholders
(cwd, pr-<number>) remain as text since they cannot be literal
TypeBox defaults.

Added:
- `minItems: 1` on ast-edit.ts `ops` array — machine-enforces what
  the .md previously stated only in prose; handler already rejects
  empty ops arrays, this adds the schema-level constraint.
- `find.ts` `pattern` description enriched with facts previously
  only in find.md (comma-separated lists, simple patterns recurse
  from cwd).

Strict-mode sanitizer: inline `default` into `description`

OpenAI's Structured Outputs strict mode rejects schemas containing
`default` with HTTP 422 ("default is not permitted"). Affects
openai, azure, github-copilot, openrouter, cerebras, together,
zenmux, and deepseek providers.

`sanitizeSchemaForStrictMode` in packages/ai/src/utils/schema/
strict-mode.ts now appends ` (default: X)` to the sibling
`description` before stripping the `default` keyword. Non-strict
providers (Anthropic, Google) still see the native keyword.

Rules:
- Inline is skipped when description already contains `(default:`
  (prevents double-inlining on recursive calls)
- Inline is skipped when no sibling description exists (no
  synthesis)
- Formatting: strings as-is (`cwd`), other values via
  `JSON.stringify` (matches the conventional text form)

CONSTRAINTS.md documents the inlining rule alongside the existing
keyword-strip rule.

Regression tests

packages/ai/test/schema-strict-mode.test.ts gains 7 `it` blocks:
- number/bool/string default types inline correctly
- falsy defaults (`false`, `""`, `0`) are not confused with absent
- `null` default goes through JSON.stringify branch
- double-inline prevention when description already says `(default:`
- no synthesis when no description exists
- nested object property with default (recursion + cache path)
- type-array `[T, null]` branch with default on outer schema
  (variant-materialization path)

23/23 schema tests pass, 541/541 ai-package tests pass,
`bun check` clean.

Rationale

|Metric                          |Value          |
|--------------------------------|--------------:|
|Per-turn prompt savings         |~2,160 tok     |
|Files touched                   |25             |
|Lines changed                   |+325 / −296    |
|Schemas migrated to `default:`  |18             |
|New regression tests            |7              |

packages/coding-agent/src/tools/python.ts

@@ -52,7 +52,7 @@ export const pythonSchema = Type.Object({
 		}),
 		{ description: "Cells to execute sequentially in persistent kernel" },
 	),
-	timeout: Type.Optional(Type.Number({ description: "Timeout in seconds (default: 30)" })),
+	timeout: Type.Optional(Type.Number({ description: "Timeout in seconds", default: 30 })),
 	cwd: Type.Optional(Type.String({ description: "Working directory (default: cwd)" })),
 	reset: Type.Optional(Type.Boolean({ description: "Restart kernel before execution" })),
 });