internal/config,server: add setParamsByMatch request filter

[asf0]

Set request parameters when a request field matches a value. Rules match on the request body rather than the model ID, so clients that send a fixed model and vary a separate field can change behaviour between requests without triggering a model swap.

macros:
  reasoning_rules:
    - key: reasoning_effort
      match: none
      set:
        chat_template_kwargs:
          enable_thinking: false
    - key: reasoning_effort
      match: high
      set:
        chat_template_kwargs:
          enable_thinking: true
        thinking_budget_tokens: 8192

models:
  my-model:
    filters:
      setParamsByMatch: ${reasoning_rules}

• rules run in order after stripParams and before setParams/setParamsByID, which keep the final say
• every matching rule applies, so a later rule overrides an earlier one
• object values merge into an existing request object, so chat_template_kwargs the client already sent are preserved rather than replaced
• match compares against the field's string form, so JSON booleans and numbers must be quoted
• protected params like model cannot be matched on or set
• supported in both model and peer filters, validated at config load

Macros can now hold maps and lists so several models can share one rule set. Without this a shared rule list needs a stray top-level YAML anchor key. Structured macros are only valid as a whole value; interpolating one into a string is a load-time error. This changes two existing tests that asserted macros were scalar-only.

Replaces the earlier reasoning-specific filter in this PR per the discussion in #958.

Fixes #958

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[greptile-apps]

Greptile Summary

Adds setParamsByMatch, a new request filter that applies parameter overrides when a top-level request field equals a configured string value. This allows clients that send a fixed model field and vary another field (e.g. reasoning_effort) to change model behaviour without triggering a model swap. Macros are extended to support map and list values so a shared rule set can be referenced by multiple models.

• MatchRule struct with config-load validation (key regex, protected-param guard, non-empty set) is wired into both model and peer filter pipelines; it runs after stripParams and before setParams/setParamsByID.
• setMergedParam performs a one-level-deep merge: when both the configured value and the existing request field are objects, sub-keys are written individually via sjson dotted paths so client-sent sibling keys are preserved.
• Macro handling is refactored to propagate errors from substituteMacroList and block non-scalar macros from being interpolated into strings while still allowing whole-value substitution.

Confidence Score: 5/5

The change is safe to merge. All three findings are edge-case nits with no impact on the documented, tested use cases.

The core logic is well-tested, protected-param checks are in place at both config-load and runtime, and the match/merge paths are covered by targeted test cases. The three findings (missing | escape in sub-key paths, one-level-only merge for nested objects, and null-vs-empty-string ambiguity in match) are all off the happy path and do not affect the primary reasoning-effort use case.

Files Needing Attention: internal/server/filters.go — the three nits are concentrated here; the rest of the changed files are straightforward.

Important Files Changed

Filename	Overview
internal/server/filters.go	Core runtime implementation of setParamsByMatch; applySetParamsByMatch and setMergedParam are well-structured, but escapePathSegment omits `
internal/config/filters.go	Adds MatchRule struct, Validate(), and SanitizedSet(); key regex, protected-param checks, and sorted output all look correct.
internal/config/macros.go	Extends macros to support map/list values, adds isScalarMacroValue guard, and propagates errors from substituteMacroList; self-reference detection via yaml.Marshal is a reasonable heuristic.
internal/config/load.go	Adds validateSetParamsByMatch hook that validates both model and peer rules at config load time; ordering and error wrapping look correct.
internal/config/config_test.go	Updates two pre-existing tests that assumed array/map macros were invalid, and adds comprehensive TestConfig_SetParamsByMatchValidation and TestConfig_StructuredMacros suites.
internal/server/filters_test.go	Adds TestServer_ApplySetParamsByMatch with 12 sub-tests covering the documented use case, merge behaviour, ordering, protected params, and ordering relative to stripParams/setParams.
config-schema.json	Adds setParamsByMatch array schema for both model and peer filters; also extends the macro value schema to allow object and array types.
internal/config/filters_test.go	Adds TestFilters_MatchRuleValidate and TestFilters_MatchRuleSanitizedSet covering edge cases for key validation and protected-param removal.

_{Reviews (2): Last reviewed commit: "internal/config,server: add setParamsByM..." | Re-trigger Greptile}