refactor(worker): share file contracts across Tools and WIP providers

Flatten shared typed Tool arguments and derive WIP parameters and checkout allowlists from core schemas. Workspace settings uses shared read/write/edit processing within its captured-read and canonical tree-CAS commit path. Identical settings edits now reject before read or commit; provider response contracts and unknown-outcome handling stay intact.

T-707 validation: root cargo check; fs-operation (58); tools (74 lib, 39 integration, 1 doctest); worker (802 lib, 109 integration); workdir --features http-client (125); yoi-workspace-server --lib workspace_config (19); cargo fmt --all -- --check; git diff --check HEAD.

docs/development/file-operations.md

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+# Shared text file operations
+
+`fs-operation::text` owns the provider-neutral read/edit/write argument contracts,
+JSON decoding, argument validation, pure text outcomes and byte-bound calculations.
+The argument schemas also supply WIP parameter declarations. Ordinary Tools flatten
+these arguments alongside their own Workdir routing fields; checkout WIP uses the
+same Tool execution functions, not a third editing implementation.
+
+Edit requires a nonempty `old_string`, a different `new_string`, and a unique
+non-overlapping match unless `replace_all` is true. Limits count UTF-8 bytes, are
+supplied by each provider, and are checked (including arithmetic/capacity overflow)
+before allocating a replacement result. Outcomes carry replacement count and byte
+size independently of persistence metadata.
+
+## Provider-owned differences
+
+- Workdir read exposes optional line offset/limit and numbered, bounded output.
+  Workspace settings read remains a whole-text read with no arguments, preserving
+  content type and digest. Line range defaults and numbered rendering live in the
+  core but are only selected by the Workdir adapter.
+- Workdir routing, attachment generation, Scope and permission identity remain in
+  Worker/Tools/Workdir. Read history and content hashes stay in the existing
+  attachment-scoped tracker. Descriptor-protected reads and checked edits/writes
+  retain their existing validator, identity and save boundary in the provider.
+- Workspace settings grants, access mode and connection lifetime remain in Backend.
+  The settings adapter binds the read to captured entry metadata and generates a
+  canonical commit using the same tree revision/digest. Decodal validation,
+  formatting and atomic multi-file persistence remain in the canonical Backend
+  commit. Content type, create/delete/rename/apply_changes and attach are settings
+  operations, not ordinary OS file operations.
+
+The core does not perform I/O, authorize anything, or own revision/existence
+mirrors. Providers invoke pure processing inside their existing consistency
+boundary; it must not be used to turn a checked edit into an unchecked
+Read–Write sequence.
+
+## External contracts
+
+Operation names, argument shapes and successful responses remain unchanged.
+Workspace settings Edit now rejects identical old/new strings before reading or
+committing (the intended behavior change). Pure text failures are explicitly
+mapped to Tool argument errors or WIP `InvalidArguments`/`ResourceLimitExceeded`
+by the adapters. A mutation's post-dispatch transport or response failure is still
+`OutcomeUnknown`; the core does not retry it or reinterpret it as a validation
+rejection.
+
+Pure policy matrices belong in `fs-operation::text` tests. Provider tests cover
+entrypoint wiring and the existing authorization, observation, checked-save,
+configuration CAS and unknown-outcome boundaries rather than copying that matrix.