docs(proxy_behavior): G4 regression-replay table for Key Tier-1

Slice 14 of the management-endpoints behavior-pinning effort. Documents
the regression-replay verification methodology + a 12-row table mapping
recent fix-PRs touching key_management_endpoints.py to the catching
scenarios in the PR1 matrix.

One canonical RED→GREEN cycle is captured verbatim — c7c3df2b02
"extend /key/update admin check to non-budget fields". Under the
parent-of-fix code, 6 scenarios in test_key_update.py flip from 200 to
403; under HEAD code, all 21 pass. The handler swap is the only change
between the two runs, confirming the matrix catches the behavior shift
the fix introduced.

The table also calls out 4 genuine coverage gaps deferred to PR2/PR3:
404-on-missing-key, budget-limit counter assertions, /key/regenerate
upperbound enforcement, and /key/list filter-param views.

Plan: https://www.notion.so/36643b8acdab8128a581ced0f6a4744d

tests/proxy_behavior/management/regression_replay/README.md

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+# G4 — Regression-replay set for PR1 (Key Tier-1)
+
+This directory documents the regression-replay verification for the
+behavior-pinning suite. For each in-scope recent fix-PR touching
+`litellm/proxy/management_endpoints/key_management_endpoints.py`, we record:
+
+- which scenario(s) in the matrix catch the behavior the fix introduced,
+- a RED-at-parent / GREEN-at-tip transcript for at least one canonical PR.
+
+## Methodology
+
+For a given fix-PR `<sha>` with parent `<parent>`:
+
+```bash
+# 1. Save current handler
+cp litellm/proxy/management_endpoints/key_management_endpoints.py /tmp/key_mgmt.HEAD.py
+
+# 2. Replace with the pre-fix version
+git show <parent>:litellm/proxy/management_endpoints/key_management_endpoints.py \
+  > litellm/proxy/management_endpoints/key_management_endpoints.py
+
+# 3. Run the catching slice — expect RED on the scenarios that flip
+DATABASE_URL=postgresql://litellm:litellm@localhost:5432/litellm_test \
+  uv run --no-sync pytest tests/proxy_behavior/management/<test_file>.py -v
+
+# 4. Restore + confirm GREEN
+cp /tmp/key_mgmt.HEAD.py litellm/proxy/management_endpoints/key_management_endpoints.py
+DATABASE_URL=postgresql://litellm:litellm@localhost:5432/litellm_test \
+  uv run --no-sync pytest tests/proxy_behavior/management/<test_file>.py -v
+```
+
+When the fix changed multiple files, the in-place swap is constrained to the
+handler module — if a referenced helper moved between modules the swap may
+not run; in that case use `git worktree add` for a clean replay.
+
+## Replay table
+
+| # | Fix SHA | Subject (truncated) | Endpoint | Catching scenarios | Verified |
+|---|---------|---------------------|----------|--------------------|----------|
+| 1 | `c7c3df2b02` | extend /key/update admin check to non-budget fields | `/key/update` | `test_key_update.py::self/{team_admin,internal_user,owner,unrelated_same_org,cross_org_user,service_account}` — all 6 flip 200→403 between parent and HEAD | ✅ RED→GREEN below |
+| 2 | `8bbc61e03c` | harden /key/update authorization checks | `/key/update` | `test_key_update.py::owner_target/*` — non-admins blocked from updating peers' keys | by-inspection (overlapping coverage with #1) |
+| 3 | `1b2756811e` | close project hijacking and key org IDOR | `/key/update` (org_id field) | `test_key_update.py` matrix asserts no row mutation on denied responses (`row.models != [MARKER]`) | by-inspection |
+| 4 | `c7c3df2b02` siblings: `f6cd0a827a` | /key/update returns 404 (not 401) for nonexistent body key | `/key/update` | NOT covered by current matrix — the matrix only exercises existing target keys. Future: add 404-on-missing scenarios. | gap (filed below) |
+| 5 | `133471f882` | double-counting bug in org/team key limit checks on update | `/key/update` (counting) | NOT directly covered; matrix asserts status only, not counts. Future: budget/limit assertions. | gap (filed below) |
+| 6 | `574633fcf1` | exclude budget_limits from deleted verification token | `/key/delete` | `test_key_delete.py` matrix verifies post-delete authentication fails — would catch a shape-of-delete change but not a budget_limits-specific bug | by-inspection (partial) |
+| 7 | `db8ef44323` | enforce upperbound_key_generate_params on /key/regenerate | `/key/regenerate` | `test_key_regenerate.py` matrix asserts status; a regen that exceeds upperbound limits would surface IF the test bodies passed disallowed params. Currently they don't. | gap (filed below) |
+| 8 | `2220f3076a` | tighten caller-permission checks on key route fields | multiple | spans /key/generate + /key/update; partial overlap with our `team_id`/`user_id` boundary scenarios | by-inspection |
+| 9 | `5190bd07eb` | extend caller-permission to service-account | /key/generate, /key/service-account/generate | service_account actor IS in our matrix; some sub-scenarios overlap | by-inspection |
+| 10 | `12005c4a02` | /key/aliases auth | `/key/aliases` | not Tier-1 (out of PR1 scope; PR3 territory) | out of scope |
+| 11 | `818c097ca9` | Self-exclusion hash mismatch | `/key/update` | partial overlap | by-inspection |
+| 12 | `daf7c0c3a8` | virtual keys team filter | `/key/list` | `test_key_list.py` filter param scenarios deferred; default-visibility scenarios already in matrix | gap (deferred) |
+
+## Verified replay: `c7c3df2b02`
+
+**Fix subject**: `fix(proxy): extend /key/update admin check to non-budget fields`
+**Parent SHA**: `662d05531d`
+**Catching slice**: `tests/proxy_behavior/management/test_key_update.py`
+
+### Parent (pre-fix) — RED
+
+```
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/team_admin]
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/internal_user]
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/owner]
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/unrelated_same_org]
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/cross_org_user]
+FAILED tests/proxy_behavior/management/test_key_update.py::test_key_update_authz_matrix[self/service_account]
+6 failed, 15 passed
+```
+
+Each of the 6 self-target scenarios returned `200` under the parent code (the
+admin check only gated budget/spend changes, so a non-admin could rewrite
+`models`) but is pinned at `403` post-fix.
+
+### HEAD (post-fix) — GREEN
+
+```
+21 passed
+```
+
+The matrix correctly flipped from 6/21 RED to 21/21 GREEN solely on the
+handler swap — confirming the suite catches the c7c3df2b02 behavior change.
+
+## Identified coverage gaps (deferred to PR2/PR3)
+
+These cells in the replay table call out genuine matrix gaps — the current
+PR1 surface does not pin the specific behavior the fix introduced. Each is
+worth a follow-up scenario:
+
+- **404-on-missing-key** (rows 4, paralleling `f6cd0a827a` and
+  `19efe556cb`) — add an explicit "actor calls /key/update with a body
+  `key` that does not exist" scenario per endpoint, asserting 404.
+- **Budget/limit counting bugs** (row 5, `133471f882`) — add scenarios that
+  read the team/org spend rows after a denied /key/update and assert no
+  counter movement.
+- **Upperbound enforcement on /key/regenerate** (row 7, `db8ef44323`) —
+  extend the regenerate matrix with at least one scenario that requests
+  params exceeding the team's `upperbound_key_generate_params`.
+- **`/key/list` filter-param view** (row 12, `daf7c0c3a8`) — PR1 only
+  pins default-visibility. Filter combinations (`team_id=`,
+  `include_team_keys=true`, etc.) belong in a follow-up.
+
+Filed as TODOs rather than blocking PR1: the matrix shape is correct,
+these are scope extensions.