fix(mcp): suggest nearest symbols on node_not_found

[devin-ai-integration]

Summary

• PrimitiveNotFoundV1 has a new suggestions field (PrimitiveSymbolLocationV1[], left out when empty). It lists up to 5 served symbols within a bounded edit distance (clamp(len/3, 1, 3)) of the requested id, simple name, or qualified name, nearest first.
• tracedecay_node, tracedecay_impact, and rename-preview misses all go through the one node_not_found_result suggester.
• The bounded edit distance now lives in tracedecay_domain::text::edit_distance_within. The CLI's nearest-tool lookup uses it in place of its own copy.

Fixes #3014

Motivation

A miss only returned "Node not found", so a caller who mistyped an id or passed a name had nothing to go on. See #3014.

Changes

• crates/tracedecay-mcp/src/handlers/graph/mod.rs: node_not_found_result(graph, node_id, occurrence) makes one cancellation-aware pass over the catalog with find_symbols. It keeps the 5 closest matches in a BTreeMap keyed by (distance, id). navigation.rs and rename_preview.rs call it.
• crates/tracedecay-contracts/.../primitive_surface.rs: adds the suggestions field. sdks/typescript/src/operations.ts and plugin/chatgpt-extension/embedded/server.mjs are regenerated (pnpm --dir dashboard run contracts:generate, extension pnpm run build). The embedded schema rejects unknown properties, so the bundle has to be rebuilt.
• crates/tracedecay-domain/src/text.rs: edit_distance_within, with unit tests.
• Unknown ids that have no nearby symbol produce the same JSON as before (existing exact not-found tests pass unchanged).

Test plan

• New behavior tests against the production MCP surface. Both fail with suggestions forced empty (the old output) and pass with this change:
  • bash scripts/require-exact-test.sh cargo test -p tracedecay --features test-transport --test mcp_suite mcp_handler_test::node_behavior_test::tracedecay_node_suggests_the_nearest_symbols_for_an_unknown_id -- --exact
  • bash scripts/require-exact-test.sh cargo test -p tracedecay --features test-transport --test mcp_suite mcp_handler_test::impact_behavior_test::impact_reports_callers_by_depth_and_refuses_invalid_requests -- --exact
• Existing exact not-found tests pass: graph_query_test::test_node_not_found, graph_analysis_test::test_rename_preview_not_found
• cargo fmt --all -- --check, python3 scripts/linux-test-partitions.py check, pnpm run check:embedded
• cargo clippy -p <crate> --all-targets -- -D warnings for tracedecay-domain, -contracts, -mcp, -cli

Checklist

• CHANGELOG.md updated: not done; release-please generates it
• No secrets, credentials, or .env files included
• Breaking changes documented: none; the field is additive and left out when empty

Link to Devin session: https://app.devin.ai/sessions/cd07d7e34d024ed2aef8a0c58184660f
Open in Devin Desktop: https://app.devin.ai/desktop/session/cd07d7e34d024ed2aef8a0c58184660f?variant=devin
Requested by: @ScriptedAlchemy

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[devin-ai-integration]

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