feat: add idempotency_token special variable per resource per session

[jeffreyaven]

Introduces idempotency_token, a UUID v4 that is generated once per resource at session start and remains stable for the lifetime of the invocation. This allows mutation queries (INSERT/UPDATE) to carry a provider-side client token that distinguishes genuine new requests from retries of the same request — a requirement for many async APIs such as the AWS Cloud Control API.

Implementation:

• CommandRunner gains an idempotency_tokens: HashMap<String, String> field populated at startup (one UUID per resource in the manifest).
• get_full_context accepts an idempotency_token: Option<&str> and injects two keys when a token is present:
  • idempotency_token (unscoped, for direct use)
  • <resource_name>.idempotency_token (scoped, for this. and downstream access)
• this.idempotency_token inside a resource's .iql file preprocesses
  to {{ <resource_name>.idempotency_token }} via the existing
  preprocess_this_prefix mechanism.

Documentation:

• template-filters.md: new "Special Variables" section documenting stack_name, stack_env, resource_name, and idempotency_token with usage examples and a tip contrasting it with uuid().
• resource-query-files.md: new "Special Variables" section with a reference table and an idempotency_token usage example.

https://claude.ai/code/session_01HAXNi38tB8nY9wiDnqVNWH

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