Pyth template completion, MCP token-bloat fix, honest 404s for /v1

[92Infinitus92]

Four changes, one commit each:

• Pyth template: 2 → 9 fields. conf, exponent, publish times, EMA values
  and posted_slot are now overridable, so scenarios can express staleness and
  confidence cases. Unit-tested against a real PriceUpdateV2 account.
• MCP: 85x smaller template payloads. get_override_templates no longer
  inlines hundreds of constant options (1.86 MB → 22 KB; it overflowed LLM
  context and TPM limits). The new search_constant_options tool resolves
  values on demand. First tests in the mcp crate. The /v1/scenarios/templates
  HTTP endpoint (studio dropdowns) intentionally keeps full data.
• Unknown /v1/ paths return JSON 404* instead of the SPA's index.html with
  HTTP 200, which masked client/API mismatches as JSON parse errors. Route
  registration is shared between server and test via configure_api.
• surfnet_timeTravel docs: absoluteTimestamp is milliseconds and jumps are
  forward-only — neither was documented.

Testing: cli 19/19, mcp 5/5, core pyth 3/3; fmt and clippy clean; live
e2e against a running surfnet.

Open questions

• Search page size is 20 (MAX_SEARCH_RESULTS): keep, change, or make it a
  tool parameter?
• Add a real GET /v1/scenarios/{id}? It grows the public API and old embedded
  UIs must not depend on it.
• Small cleanup PR for three pre-existing nits (legacy error convention in
  older MCP tools, dead Arc app_data in cli/http, HEAD 404s on GET routes)?

Greptile Summary

This PR bundles four focused changes: expanding the Pyth PriceUpdateV2 override template from 2 to 9 fields, shrinking MCP template payloads 85× by summarising constant options and adding an on-demand search_constant_options tool, returning proper JSON 404s for unknown /v1/* paths, and correcting surfnet_timeTravel docs (milliseconds, forward-only).

• Pyth template gains conf, exponent, publish_time, prev_publish_time, ema_price, ema_conf, and posted_slot; a detailed LLM-context block guides staleness-scenario construction. All 8 fields are covered by a new round-trip test.
• MCP payload reduction extracts compact_template_json (shared between the get_override_templates tool and the MCP resource handler), introduces search_constant_options for on-demand option lookup, and adds 5 unit tests. The HTTP /v1/scenarios/templates endpoint is intentionally left with full data.
• JSON 404s are implemented by registering a web::scope("/v1").default_service(…) catch-all inside a shared configure_api helper; the test covers GET, POST, and a known-good path.

Confidence Score: 5/5

• This PR is safe to merge. All four change areas are well-tested, the routing change is validated end-to-end, and the new MCP tool has no side-effects on existing behaviour.
• Every changed code path has direct test coverage: the Pyth byte-layout is pinned by a round-trip test, the 404 routing is exercised for GET, POST, and a known-good path, the MCP payload reduction is covered by five unit tests including a schema-shape assertion, and the U16BeRef string-parsing is guarded by three property tests. The docs and YAML changes carry no runtime risk.
• No files require special attention.

Important Files Changed

Filename	Overview
crates/mcp/src/surfpool/mod.rs	Adds compact_template_json helper (eliminates the two duplicate inline-mapping blocks), new search_constant_options tool with error handling for unknown template/constant, and 5 tests covering schema shape, case-insensitive search, truncation, and error paths. Logic is sound; metadata is included verbatim in results (flagged in a previous comment).
crates/cli/src/http/mod.rs	Extracts configure_api so the route graph is shared between the live server and tests. Adds the /v1 scope default-service 404 handler and a test that validates GET, POST, and a known-good route (200). Routing order is correct: specific resources registered before the scope win in actix-web's trie matcher.
crates/core/src/scenarios/protocols/pyth/v2/overrides.yaml	Adds 7 new overridable properties and a comprehensive LLM-context block documenting scaling conventions, forward-only time semantics, and a step-by-step staleness-scenario recipe. Documentation is accurate and well-structured.
crates/core/src/surfnet/locker.rs	Extracts the Pyth fixture bytes into pyth_price_update_v2_fixture(), refactors the import block, and adds test_get_forged_account_data_overrides_all_pyth_price_feed_fields that round-trips all 8 template fields through the forge path and decodes the result. Tests are thorough and pin against the real byte layout.
crates/types/src/scenarios.rs	Extends PdaSeed::U16BeRef to accept decimal strings (needed when MCP tools pass config indices as JSON strings). Three new tests cover the happy path, rejection of out-of-range/non-numeric strings, and rejection of non-integer JSON types.

Sequence Diagram

sequenceDiagram
    participant LLM as LLM Client
    participant MCP as MCP Server
    participant Registry as TemplateRegistry

    LLM->>MCP: get_override_templates()
    MCP->>Registry: registry.all()
    Registry-->>MCP: Vec of OverrideTemplate
    Note over MCP: compact_template_json - constants summarised as optionsCount, options array omitted
    MCP-->>LLM: templates with id, properties, constants summary, llmContext

    LLM->>MCP: search_constant_options(templateId, query)
    MCP->>Registry: find template by id
    Registry-->>MCP: OverrideTemplate
    Note over MCP: iterate constants sorted, case-insensitive match, cap at MAX_SEARCH_RESULTS=20
    MCP-->>LLM: results with value field, totalMatches, truncated

    LLM->>MCP: create_scenario(templateId, values with resolved feed_id)
    MCP->>MCP: POST surfnet_registerScenario
    MCP-->>LLM: success with studioUrl

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[92Infinitus92]

Re-signed the branch — every commit is GPG-verified now. Nothing else changed: the tree hash is identical to the previous tip, git diff between old and new is empty, and the merge with develop kept its original second parent.

The hashes referenced in the threads above moved: b8aad68 → 07642b0, 838cad6 → f2f0a31, 77db914 → e052847. The stacked branch was rebuilt on the new base, so c5350e5 → 4d648c1.