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+# Plan
+
+1. Export the capture parser from `environmentSource.ts` so a probe loads like a capture.
+2. `environmentCompareMatch.ts`: a probe request to a tool and its arguments.
+3. `environmentCompareIds.ts`: the id map, natural-key pairing, learning from two answers, translating arguments.
+4. `environmentCompareDiff.ts`: normalisation and categorised differences.
+5. `environmentCompare.ts`: per probe, reset the state, answer each request, compare and learn; the report.
+6. `rea environment-compare` in `src/cli/environmentCommands.ts`, documented in `docs/agent-environments.md` and
+   `docs/cli.md`.
+7. Tests: matching, pairing, normalisation and categories as unit tests; the command over a fixture capture and probes.
+8. Verification on VMs: six applications brought up and seeded as for their capture, reset from a snapshot per sequence,
+   driven by a script that records each sequence as a HAR; baseline reports per environment.
diff --git a/docs/specs/agent-environments/fidelity-compare/spec.md b/docs/specs/agent-environments/fidelity-compare/spec.md
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+# Compare an environment with the application it came from
+
+Issue: https://github.com/morluto/rea/issues/4933
+
+## Outcome
+
+An environment is only as useful as it is faithful: an agent trained or graded on it should meet the behaviour of the
+application it was captured from. REA checks an environment only against its own capture, so nothing says how far it
+drifts from the application on calls the capture did not make, after writes, or on errors.
+
+`rea environment-compare` measures that. It takes an environment (a manifest and its capture Evidence) and one or more
+**probe captures**, each a recording of one call sequence made against the live application, and reports how many of the
+probe's calls the environment answers as the application did, which tools disagree and how.
+
+The command only reads Evidence: it makes no network call. Whoever records the probes drives the application with its own
+credentials and resets it between sequences.
+
+## Requirements
+
+- Inputs: the manifest Evidence, its capture Evidence (`--evidence`), and one or more probe capture Evidence files
+  (`--probe`, repeatable), each `inspect-web-network-capture` or `capture-browser-scenario` Evidence of one sequence.
+- Each probe is one sequence run against a freshly reset application. Before each probe the environment's state is reset,
+  so sequences are independent on both sides.
+- Requests are taken in the probe's order (start time, then ordinal). A request is matched to the manifest tool of the
+  same method whose path template it fits with the most literal segments; format-rule parameters must fit their format.
+  Path values, query values the tool takes and a JSON body become the tool's arguments.
+- A request no tool matches is reported `no-tool`; a matched tool the environment does not offer, such as a write it
+  withholds, is reported `not-served`. Neither is answered.
+- Ids differ between a re-seeded application and the capture. The comparison maps them:
+  - seeded entities pair across the two answers by a natural key: a field present on every element of both arrays whose
+    string values are unique on each side and shared between them;
+  - identifier fields (`id`, `uuid`, names ending in `id` or `_id`) of paired objects, and of the two answers to the same
+    call, map the live value to the environment's value; a create's two answers map the new ids;
+  - path, query and body values equal to a mapped live id are translated before the environment answers.
+    A path value the map does not know, and the environment's state does not hold, is reported `unmapped-id`.
+- Answers compare after normalisation: mapped ids compare equal; two clock values (ISO-8601 strings, or epoch numbers under
+  time-named fields) compare by format only; two different generated values (both UUIDs, or both of one length and the
+  same character classes with a digit) that neither side maps compare equal and are counted.
+- A step agrees when the statuses are equal and the normalised bodies are. Differences are categorised: `status`,
+  `missing-field` (the application had it), `extra-field`, `value`, `length`, `order`, `clock-format`, `refused` (the
+  environment refused the call), `not-served`, `no-tool` and `unmapped-id`, each with a JSON pointer and short values.
+- The report gives agreement overall, per probe and per tool, the counts per category, the ids mapped and the values
+  normalised, and each step's differences (at most 20 per step).
+
+## Non-goals
+
+- No network access, no credentials, no reset of the application: probes are recorded outside REA.
+- No generation of call sequences; a later change generates them where the environment disagrees.
+- No change to how environments serve.
diff --git a/docs/specs/agent-environments/fidelity-compare/tasks.md b/docs/specs/agent-environments/fidelity-compare/tasks.md
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+# Tasks
+
+- [x] Record the outcome, requirements and non-goals.
+- [ ] Load probes as captures.
+- [ ] Match probe requests to tools.
+- [ ] Map ids and translate arguments.
+- [ ] Normalise and categorise differences.
+- [ ] Compare per probe and report.
+- [ ] Add the command and its documentation.
+- [ ] Add unit and command tests.
+- [ ] Run the gates.
+- [ ] Measure six environments against their live applications and record the results.