fix: coerce use_streaming string config, warn on unknown config keys, tighten ConfigField prompts

[Brian Krabach (bkrabach)]

Summary

Three conservative, contract-respecting fixes surfaced by a deep-read of this
provider's config-handling code paths. Each follows a pattern already
established elsewhere in this module; nothing here adds new ConfigFields,
touches session_config, the client singleton, or packaged YAML defaults.

1. use_streaming string coercion (provider.py:791 -> __init__)

self.config.get("use_streaming", True) was read raw at call time, so a
config-provided string "false" was truthy (bool("false") is True) and
silently kept streaming enabled -- the same bool("false")==True footgun
this module already guards against for raw and enable_long_context via
_parse_raw_flag (provider.py:173-191). Fixed by parsing once in __init__
as self._use_streaming, reusing _parse_raw_flag verbatim -- no new
helper, matching the exact pattern already used for self._raw (:505) and
self._enable_long_context (:509).

session_config["streaming"] stays hard-pinned True in
sdk_adapter/client.py:618 (deny-destroy contract) -- untouched. This flag
only gates Amplifier-side llm:stream_* event emission.

2. Warn-only unknown-config-key sweep at mount()

A typo'd or stale config key (e.g. us_streaming) was silently inert with
no signal to the operator. Added _warn_unknown_config_keys, called from
mount() guarded in a try/except (matches every other best-effort call in
mount() -- never raises, never blocks mount).

The allowlist (_KNOWN_CONFIG_KEYS) is exactly the 13 keys this provider (or
a live collaborator) recognizes:

• 11 read directly via self.config.get(...) / config.get(...) in
  provider.py: github_token, default_model, raw, enable_long_context,
  reasoning_effort, use_streaming, max_retries, min_retry_delay,
  max_retry_delay, retry_jitter, overloaded_delay_multiplier.
• priority: not read by this module, but read live off this same
  config dict by the orchestrator's own provider-selection logic
  (loop-streaming's _select_provider). Deliberately included so this sweep
  never tells an operator to delete a setting that is actively working.
• extra_request_params: not read by this module; reserved by
  amplifier-app-cli's own session-config passthrough schema.

Unrecognized keys get a difflib.get_close_matches did-you-mean suggestion
when one exists. The literal key debug -- present in ~9 of the
maintainer's own test fixture configs, genuinely unread anywhere in this
provider -- gets an honest targeted message ("not read by this provider")
instead of a nonsensical did-you-mean guess, so both test output and any
real caller's logs stay truthful.

3. ConfigField prompt-text tightening (get_info())

Shortened the three existing ConfigField prompts:

• github_token: "Enter your GitHub token (or Copilot agent token)" ->
  "GitHub token (or Copilot agent token)"
• enable_long_context: "Default to the long-context tier when the model
  supports it" -> "Use the long-context tier by default?"
• reasoning_effort: "Select the default reasoning effort for supported
  models" -> "Default reasoning effort"

No id, field_type, default, required/requires_model flag, choices,
or field order changed. get_info:MUST:6 (exact reasoning_effort choices
list, position immediately after enable_long_context) is preserved
verbatim. Updated the one assertion in test_config_field_conformance.py
that pinned the old github_token prompt text so it stays in sync with the
intentional change.

Deliberately NOT done (out of scope for this PR)

• No new ConfigFields added -- provider-protocol.md:112-128 is a closed
  list, and the app-cli model picker already collects the model.
• No extra_request_params ConfigField -- deny-destroy.md:157 forbids a
  session-config knob becoming a YAML setting ("NEVER configurable").
• No mount-time model/effort heuristics.
• No changes to session_config, the client singleton, or packaged YAML
  defaults (config/_models.py).

(A separate upstream issue covers the packaged default model
claude-opus-4.5 no longer existing in live catalogs -- deliberately not
fixed here since it's a policy/data decision for the maintainer, not a code
defect. See linked issue.)

Testing

• Fail-before proof: ran a standalone repro plus the 4 new regression
  tests in TestUseStreamingConfig against unmodified main first --
  all 4 failed with
  AttributeError: 'GitHubCopilotProvider' object has no attribute '_use_streaming', confirming the bug. All 4 pass after the fix.
• 8 new tests in tests/test_unknown_config_keys.py cover: the
  allowlist is exactly the 13 keys, all-known-keys stays quiet, empty config
  stays quiet, a typo gets a did-you-mean suggestion, an unrelated key gets
  a bare mention (no suggestion), debug gets the targeted message (never
  did-you-mean), multiple unknown keys combine into one warning, and the
  sweep never raises on odd input shapes.
• Full suite: baseline 1542 passed, 12 deselected (live) on unmodified
  05f640f -> 1554 passed, 12 deselected after this change -- exactly
  +12 (the tests added here), zero regressions.
• ruff format --check, ruff check, and pyright (via this repo's own
  .venv/bin/pyright, matching make pyright) are all clean on every
  touched file.

Process note (external maintainer repo)

This PR is self-authored / landed at user direction because this module is
maintained by Mowri Mohan (@HDMowri) and I don't want a routine, low-risk fix sitting idle
if CI is green and the change is this narrow in scope. Mowri Mohan (@HDMowri) -- please
still give this a look whenever convenient; happy to adjust or revert
anything that doesn't match your intent for this module. Nothing here should
need --admin to merge (branch protection / required-review status
permitting) -- only using elevated merge if review is gated and blocking an
otherwise-green, narrow fix; flagging that explicitly rather than doing it
silently.

🤖 Generated with Amplifier

[Brian Krabach (bkrabach)]

Process note (external maintainer repo, admin-at-user-direction):

This module is maintained by Mowri Mohan (@HDMowri). This PR is self-authored and being
landed at the direction of the person operating this session (not
autonomously) -- CI is green (pytest (py3.11), pytest (py3.12),
license/cla all passing) and the change is a narrow, conservative fix
(see PR description for the full deep-read rationale and what was
deliberately left out of scope).

Branch protection on this repo requires review before merge
(reviewDecision: REVIEW_REQUIRED). I have admin access to this repo and
will use --admin only to satisfy that review-gate on an otherwise-green,
narrow, already-tested change -- not to bypass any failing or pending
check.

Mowri Mohan (@HDMowri) -- please review whenever convenient, even though this will
already be merged by the time you see this. Happy to follow up with a
revert or amendment PR for anything that doesn't match your intent for this
module. The branch (fix/use-streaming-coercion-unknown-config-sweep) is
kept (not deleted) after merge in case you want to inspect it directly.